A study of 51 males being followed in the Wellesley Hospital Toronto SLE Clinic examined the questions of whether SLE in males was similar to that in females and whether affected males differ from unaffected males with respect to their maleness and sex hormone profile. Fifty of the men were phenotypically males, and one was known to have Klinefelter syndrome (karyotype 47 XXY). All had four or more 1982 revised criteria for SLE. Fifty females matched with respect to age and duration of disease were used as controls. In examining the spectrum of the disease, 21 clinical and laboratory manifestations were assessed. Although neurologic involvement, alopecia, and thrombocytopenia were less common and pleuritis more common in the males, none of these was statistically significant. Comparison of disease severity revealed only one statistically significant difference: the mean duration of corticosteroid usage was longer in the females. There was also a tendency for cytotoxic agents to be used more frequently in the females. It was thus concluded that spectrum and severity of the disease tended to be similar in males and females. The frequency of positive family histories for SLE and other autoimmune diseases was similar in males and females. The age of onset tended to be more evenly distributed in males than in females, with one quarter of the males diagnosed after the age of 50. HLA typing revealed increased frequencies of the B8 and DR3 antigens in the SLE males compared with normal controls, as had previously also been shown for SLE populations with a female preponderance.(ABSTRACT TRUNCATED AT 250 WORDS)