Fifty consecutive patients infected with human immunodeficiency virus type 1 (HIV-1) were evaluated regarding the prevalence of HIV-related myopathies and the relevance of zidovudine-related mitochondrial myopathy. Disease stage, total lifetime intake of zidovudine, anthropometric and nutritional parameters, muscle strength, and histochemical and immunohistochemical findings in muscle specimens were recorded. The series was divided into two groups, patients with a total lifetime intake of zidovudine under 200 gm and those with a total lifetime intake over 200 gm. A control group included 50 healthy people matched for age and sex. HIV-related myopathy was defined by the presence of at least one of the classic pathological reactions in muscle, while zidovudine-related myopathy was defined by the presence of ragged red fibers in any percentage. Lower values of the nutritional parameters were detected in the HIV cohort, when compared with normal control values. HIV-related myopathy was detected in 13 (26%) of the 50 patients. There were no differences between groups except for the development of mitochondrial myopathy that occurred in 1 of the 26 patients in Group 1 and in 16 of the 24 in Group II. Six patients who had a total intake of more than 200 gm of zidovudine and demonstrated red ragged fibers in their muscle specimens were absolutely asymptomatic. There was a positive correlation between total intake of zidovudine and the percentage of red ragged fibers in muscle biopsy specimens.