We studied the reliability and validity of the World Health Organization quality of life (WHOQOL) assessment instrument in patients with human immunodeficiency virus (HIV) infection. WHOQOL-BREF was used to assess 136 HIV-infected outpatients. The results were analyzed and compared with data from 213 healthy persons. The Cronbach's for internal consistency ranged from 0.74 to 0.85 across domains in HIV-infected patients. The test–retest reliability ranged from 0.64 to 0.79 across domains at average 4-week retest interval. Factor analysis identified four major factors: social, psychological, environment, and physical, consistent with the four domains of the instrument. The scores of all four domains correlated positively with self-evaluated health status and happiness (r range: 0.52–0.60 and 0.55–0.73 across domains, respectively), and correlated negatively with the number and severity of symptoms (r range: –0.40 to –0.47 and –0.41 to –0.52, respectively). The scores of physical, psychological and social domains, but not the environment domain, discriminated between healthy persons and HIV-infected patients (all p < 0.01).="" we="" conclude="" that="" the="" whoqol-bref="" can="" be="" a="" useful="" quality-of-life="" instrument="" in="" patients="" with="" hiv="">