Not everyone who seems to qualify for a green card (U.S. lawful permanent residence) actually receives one. The denial rates vary by category of green card, and they vary widely -- statistics of denial rates between 6% and 50% are commonly seen.
The reasons for the immigration authorities (either the U.S. State Department or U.S. Immigration and Citizenship Services, known as USCIS) to deny a green card vary widely as well. In addition to basic issues of eligibility, U.S. immigration laws contain long lists of grounds of inadmissibility, meaning characteristics that prohibit someone from entering the U.S., whether they're applying for a visa or a green card or other form of entry. The grounds of inadmissibility that tend to cause green card applicants the greatest problems are discussed below. Some grounds can be corrected or waived (legally forgiven), but you'll want a lawyer's help to prepare a waiver application.
The immigration laws are quite strict in requiring that applicants fit themselves into narrow categories of eligibility. So, for instance, someone requesting a green card based on having a U.S. citizen stepparent might be denied if it turns out that the parents' marriage took place after the child was age 18. Or, someone might be denied a green card as an investor if he or she can't prove that the investment won't create at least ten new jobs in the United States.
Also realize that just getting through the process of obtaining a green card can be difficult. Some people's applications fall apart because they fail to meet deadlines, to attend their interview for an immigrant visa or green card, or to supply the documentation that the U.S. immigration authorities ask for.
If you have violated U.S. immigration laws, for example by committing fraud in order to get a visa, entering the United States illegally (especially more than once), entering as a stowaway, or helping smuggle aliens across the U.S. border, your green card application may be denied. In some cases the denial is permanent, in others you won't be allowed a green card for a period of years.
Drug traffickers, drug addicts, and drug abusers will be denied a green card. In some cases no conviction is required -- you just need to have admitted to abusing a drug. One-time experimentation might be okay, but not much more.
In order to limit the number of people coming to the U.S. who will need economic support from the government, immigrants who are deemed likely to become "public charges" -- that is, require government assistance -- will be denied green cards. This usually comes up in the context of family-based immigrant petitions.
Family petitioners (sponsors) will have to file an Affidavit of Support promising to be financially responsible for the immigrant for approximately ten years. The petitioner will also need to show a level of income and assets sufficient to support the immigrant and family at 125% above the U.S. poverty line. To see exactly what income levels are required (they're updated annually), see USCIS Form I-864P. If the petitioner's income and assets are not enough, the application can be supplemented by showing assets held by the immigrant, or by having a household member or other friend or relative additionally promise to provide support.
A number of crimes will lead to denial of a green card, including money laundering, prostitution or soliciting a prostitute, and "crimes of moral turpitude," a subjective standard which may cover everything from murder to rape (including statutory rape) to bribery to perjury. In addition, having two convictions on record for any type of crime is a ground of inadmissibility.
Similarly, people considered to be spies, terrorists, saboteurs, or to have the intention of overthrowing the U.S. government, and so forth are inadmissible.
Do not attempt to analyze on your own whether a certain crime or security violation makes you ineligible for a green card. There is no set list -- you'll need a lawyer's help with the analysis. Also realize that, even in some cases where you may have been told that a crime would be wiped off your record, the immigration authorities may still count that crime against you.
In an effort to protect the health of the people of the United States, certain health problems can lead to a denial of a green card -- which the immigration authorities will find out about by having you undergo a physical examination as part of the application process. Having a communicable disease of public health significance, or a physical or mental disorder that threatens the property, welfare, or safety of others, are grounds for denial.
Tuberculosis is the main problem in terms of communicable diseases (HIV used to be, but no longer). However, the physical or mental disorder ground is much broader. For example, if you have a DUI on record and the immigration authorities discover that you're an alcoholic, they may decide that this presents a danger to others, and that you are inadmissible.
A person who has not had required vaccinations can also be denied a green card. That's why you'll be asked to have any vaccinations you lack done at the end of your required medical exam.
See the following articles to learn more about dealing with the various types of green card application denials: