OBJECTIVE To develop a multidimensional classification of sexual partnerships. METHODS Eighty-two female subjects (ages 15-20 years; 77% African American) used coital logs to record dates of 1265 coital events, partner initials, and condom use. Logs were collected at 1-, 3-, 9-, 15-, and 21-month return visits. Three adolescent health professionals independently classified partnership patterns of each subject; classification schemes were revised until complete consensus for each subject was obtained. RESULTS Complete agreement in partnership classification was reached after 3 rounds. The consensus partnership classification had three dimensions: number (1, > or = 2 partners), pattern (1 partner, serially exclusive, concurrent), and duration (any partnership < or = 21 days, all partnerships >21 days). A total of 34 of 82 (34%) of subjects had > or = 2 partners; 11 of 34 (32%) had concurrent partnerships. Twenty of 82 (24%) had only partnerships lasting >21 days. Condom use was less common for subjects in only longer-term (>21 days) partnerships, but did not significantly vary by number or pattern. CONCLUSION Multiple dimensions of adolescent sexual partnerships may be identified. Detailed research and clinical assessments along these dimensions may improve understanding of protective behaviors such as condom use.