Recent studies on the association between obesity and prostate cancer appear to be in conflict. A recent prospective cohort study reported that the incidence of prostate cancer was lower among obese men under the age of 60 years and among those men with a family history of prostate cancer. Similarly, a case-control study found obesity was inversely associated with prostate cancer risk in men aged 40-64 years. However, several prospective cohort studies found that obese men are more likely to die from prostate cancer than non-obese men. Finally, two recent studies found that among men with prostate cancer, obese men were more likely to have a biochemical progression after surgery. We postulate that by closely examining the comparison groups used in these studies, these findings may, in fact, be in agreement. Specifically, this paradox within the literature may result from the possibility that obesity influences the development of aggressive (i.e., higher stage, higher grade, recurrence, death) and non-aggressive disease differently. We suggest that obesity may reduce the risk of non-aggressive disease but simultaneously increase the risk of aggressive disease. Finally, additional methodological issues are discussed that investigators need to be aware of to be able to draw inferences across studies of obesity and prostate cancer outcomes.