To validate the use of multiplex case families in studying the pathogenesis of systemic lupus erythematosus (SLE), we investigated the pattern of familial SLE in relation to sporadic SLE in the highly consanguineous Kuwaiti population. We sought to determine whether familial and sporadic SLEs have the same clinical and serological features. We compared 21 cases of familial SLE in 21 families with 42 non-familial SLE controls matched for age, sex and duration of disease. Twenty-one families, in which the diagnosis of SLE was verified in at least two relatives, were included in the study. The diagnosis was made according to the revised 1982 American College of Rheumatology criteria. There were no significant differences in clinical features or serological manifestations between familial SLE cases and their matched controls. However, our results showed that the frequency of La/SSB antibodies was higher in the sporadic group (P = 0.048), although this was not significant after application of Bonferroni's correction for the number of comparisons. Familial cases of SLE were more likely to present at younger age of 20 years and sporadic cases at 26 years (P = 0.006). The prevalence of familial SLE was 27.4%. We have found that familial and sporadic cases of SLE are broadly similar, and it is justified to include multiple case families in genetic studies.