In this analysis the aim was to determine the independent effect of moderate to severe weight loss prior to an AIDS diagnosis on survival after AIDS. The study was conducted as part of the Multicenter AIDS Cohort Study (MACS), a longitudinal study of HIV-1-seropositive gay or bisexual men. Measured weight and self-reported weight loss data were collected semiannually from 1984 through 1993. The study population included 962 HIV-1-seropositive men who developed clinical AIDS during the follow-up period. Median survival after AIDS was significantly lower for men with measured weight loss of > or = 4.5 kg 3-9 months and 3-15 months prior to AIDS, or who had lost > 10% of their baseline body weight compared with men with less weight loss or weight gain. Men with self-reported unintentional weight loss of > or = 4.5 kg 3-9 months prior to AIDS had significantly poorer survival (median = 1.05 years vs. 1.48 years; p = 0.0001) compared with men not reporting weight loss. After adjusting for potential confounding factors, men in the high measured weight loss group 3-9 months prior to AIDS still had significantly poorer survival [relative hazard (RH) = 1.36; p = 0.02]. Similar trends were seen for the two longer intervals prior to AIDS (RH = 1.38, p = 0.01; and RH = 1.50, p = 0.02, respectively). Men who self-reported weight loss > or = 4.5 kg 3-9 months prior to AIDS also had significantly poorer survival after AIDS (RH = 1.43; p = 0.002) in multivariate analysis.(ABSTRACT TRUNCATED AT 250 WORDS)