The risk of HIV/AIDS infection among Puerto Ricans is especially pronounced, with injection drug use identified as one of the main risk factors among this group. Additionally, Puerto Ricans have been known to extensively travel between Puerto Rico and New York, which is important to understand when developing health care-related interventions. The authors note that geographical differences between New York and Puerto Rico must be considered when assessing risk factors. As such, the authors conducted a dual site study in which determinants of injection risk factors and sex-related risk factors were examined among Puerto Rican drug users. Both quantitative and qualitative methodologies were employed in order to enhance cross-site comparability of the data. Indeed, one of the primary purposes of this article is to describe the use of both types of methodologies. Qualitative methods included observations, focus groups, ethnographic mapping, and face-to-face interviews. Survey data comprised the quantitative methodology. Results of the survey data revealed that there were high levels of risk behaviors in both sites, with significantly higher levels of risk reported in Puerto Rico. However, the main results reported by the authors had to do with the use of both types of methodologies. The use of one type of methodology enabled the researchers to identify issues that needed to be addressed with the other methodology. As such, their study became more complete as missing or interesting data were rounded by the use of both quantitative and qualitative methods. Tables, references