This study describes the clinical and laboratory features and the natural history of 31 patients with late onset (in the sixth decade or later) systemic lupus erythematosus (SLE). Patients with late onset SLE constitute a distinct subset of the general lupus population that accounts for approximately 12 per cent of the cases. Advanced age modifies the expression of SLE in terms of clinical presentation (pleuritis and/or pericarditis are the most common presenting manifestations) and pattern of organ involvement (pulmonary abnormalities are more common, whereas lymphadenopathy, Raynaud's phenomenon, neuropsychiatric disease, alopecia and skin rash are less common). Because SLE is not usually considered to be a disease that affects the elderly, and because the pattern of SLE in the older age group may differ substantially from the seen in younger patients, there is often a delay in diagnosis (median of 10 months, with a delay of over one year in 32 per cent of patients). In light of the high incidence of steroid complications in older patients (40 per cent in our series), and because these patients with SLE have a relatively good prognosis (five year survival of 92.3 per cent; nine year survival of 83.1 per cent), therapy should be more conservative in late onset SLE.