There is evidence suggesting that clinical manifestations and severity in systemic lupus erythematosus (SLE) are associated with age, sex and ethnicity. The influence of genetic factors, particularly HLA antigens, on disease expression is revealed by the diversity of clinical conditions in patients from different ethnic groups. The aim of this work was to analyze the impact of demographic factors on SLE expression in the Spanish population. Therefore, a retrospective analysis was undertaken of clinical records of 307 patients diagnosed in three Rheumatology Services, with a mean follow-up of 79 months. The distribution of clinical manifestations according to age and sex was studied and compared with those observed in other ethnic groups. The results show the influence of sex and age on our patient population. Thus, female had a higher frequency of malar rash, photosensitivity and lymphopenia. Males had a higher CNS and renal involvement. Patients under 15 years had a higher involvement of CNS and kidney. Patients under 15 years had a higher frequency of nephropathy, hematological, cutaneous and CNS changes. Patients older than 50 had a higher frequency of pleuropericarditis, but without renal involvement. Our ethnic group expressed a disease with a severity similar to that observed in north-european caucasians, higher than in north-american caucasians and lower than in south-american caucasians, asiatic and africans. In conclusion, patients with SLE from the south-european ethnic groups express a clinical picture with characteristics and severity similar to those observed in europeans from other latitudes and different from those reported in other ethnic groups.