The purpose of this study was to determine gender and age differences and interaction effects on the quality of life (QoL) domains in a sample of Portuguese HIV-positive patients, and to examine to what degree psychopathological symptoms are associated with QoL in addition to sociodemographic and clinical variables. The sample consisted of 1191 HIV-positive patients, and measures included the WHOQOL-HIV-Bref and the Brief Symptom Inventory. Controlling for clinical status, there was a significant effect of gender on QoL. Women reported lower scores of Psychological and Spirituality QoL. Younger patients reported higher scores on Physical and Level of Independence domains. Age by gender interactions emerged on all domains of QoL except on the Level of Independence domain. Overall, women over 45 years old showed lower QoL scores. Psychopathological symptoms contributed significantly to the variance of all QoL domains. Gender differences in the association of HIV infection with QoL and psychopathological symptoms seemed to be modulated by age. Understanding gender and age differences (and their interaction) may provide potentially useful information for planning interventions to improve QoL and mental health among people infected with HIV/AIDS, especially among older women.