Janulis P, Goodreau SM, Birkett M, et al. - Studies have described volatility in sexual contact rates as an important factor affecting HIV transmission dynamics. They suggest one-time partnerships as particularly relevant given the potential to quickly accumulate a large number of contacts. Researchers sought to present the much needed data on temporal variation in one-time partners to provide better insight in behavioral dynamics and enhance the accuracy of transmission models. A longitudinal cohort study of young men who have sex with men and transgender women in Chicago was used to obtain data for this study. Sexual network data were provided by participants every 6 months for 2 years. Casual partnerships were noted to be positively linked and main partnerships were noted to be negatively linked with one-time partnership rates. A small positive correlation remained between prior one-time partnerships and the current number of one-time partnerships. Although there was preponderance of a low number of one-time partners, young men who have sex with men and transgender women show substantial variation in one-time partnership rates. Accordingly, they suggest that it is insufficient to focus on high contact rate individuals alone to determine periods of highest risk.