Two large outbreaks of Q fever occurred in 1987 and 1988 in an agricultural community for the rehabilitation of drug users. Approximately 40% of the residents were human immunodeficiency virus (HIV)-positive. Two hundred thirty-five residents presented with clinical evidence of a flulike syndrome that was confirmed to be Q fever; moreover, a large proportion of residents developed an asymptomatic infection. Clinical signs and symptoms were rather nonspecific: fever, malaise, and muscle pain that were often associated with pulmonary symptoms. Single or multiple opacities were detected, with mild interstitial inflammation evident on chest roentgenograms. The source of infection was the sheepfold, which is part of the stock-farming activity of the community. Both outbreaks occurred just after lambing had begun. Residents who were exposed during the first epidemic were protected in the second one. The attack rate among HIV-positive residents was significantly higher than that among HIV-negative residents in the first outbreak, whereas only a slight, marginally significant difference was observed in the second outbreak. The clinical features of Q fever did not differ between HIV-positive and HIV-negative individuals. No cases of relapse or chronic disease were observed.