This study Identifies the possible risk factors for osteonecrosis (ON) in a homogenous group of early system lupus erythematosus (SLE). Forty-six consecutive SLE patients (<5 years duration) followed at the Lupus Clinic, were enrolled between 2004 and 2005. An extensive clinical and laboratory evaluation using a standard electronic protocol established since 1999, including osteonecrosis symptoms and appropriate magnetic resonance imaging (MRI), were carried out at 1-6 months intervals. All other asymptomatic for osteonecrosis patients at study entry underwent MRI. ON confirmed by MRI was found in 10 of 46 patients (22%). Age, disease duration, clinical vascular features, frequency of thrombophilia and hypofibrinolysis factors and the lipoprotein profile were comparable in patients with and without osteonecrosis (P > 0.05). Remarkably, the frequency of patients with system lupus erythematosus disease activity index (SLEDAI) > or =8 in the previous year of osteonecrosis clinical diagnosis was significantly higher when compared to patients without this manifestation (60.0% versus 19.4%, P = 0.011), supported by the higher glucocorticoid cumulative dose in the same period (P = 0.045). In contrast, these two parameters evaluated in 13th-24th months preceding osteonecrosis diagnosis were similar in patients with and without osteonecrosis (P > 0.05). In the logistic regression analysis only SLEDAI remained as an independent risk factor for ON (OR = 6.78, CI = 1.05-43.55, P = 0.04). Disease activity in the previous year of ON clinical diagnosis is the main predictor factor for the development of this complication in early SLE.