My bf & his 17-yr-old son are undocumented. If I married him and filed to adopt his son b4 his 18th b-day would he qualify for green card?

As you are a US citizen, marrying your boyfriend before his son turns 18 would automatically make him your stepchild for immigration purposes. You could then also petition for him as your child. If your boyfriend and his son entered legally, they would likely be able to adjust status in the US. If they entered illegally, they would generally not be able to adjust status. They might, however, be able to qualify for the Administration's I -601A provisional waiver program under which you would file I-130 relative petitions for them, and once approved, they would file I-601A waiver applications based upon extreme hardship to you if the applications were refused. The waiver applications would be adjudicated in the US and if approved, they would begin to process their cases with the American Consulate in their home country for immigrant visa interview. With approved waivers, the interviews would in all likelihood be passed. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.