I remember first hearing about this quite a few years ago. Apparently, someone who was studying lung cancer patients had a few people among his study subjects (about 4, I think) that didn't have any known risk factors (didn't smoke, didn't live with a smoker, that kind of thing). The only thing that he could find that they had in common was that they had all owned pet birds at some time in their lives. He was the first to suggest a link between birdkeeping and cancer; his report was published in 1988 (according to an article I found in a Google search). There have been several studies since then, trying to determine whether or not there really is a link. A few have suggested that there may be, others have come to the conclusion that there isn't. Since virtually all of the study subjects that had been bird owners also had at least one other risk factor, it hasn't been possible to totally isolate bird ownership to determine how much risk (if any) it actually represents. As near as I can tell, the best anyone can say is that smokers that keep birds may be slightly more likely to develop lung cancer, than those that don't.
