Data from the International Collaborative Gaucher Group Gaucher Registry were analysed to assess the relationship between enzyme replacement therapy with imiglucerase (ERT) and incidence of avascular necrosis (AVN) in type 1 Gaucher disease (GD1), and to determine whether the time interval between diagnosis and initiation of ERT influences the incidence rate of AVN. All patients with GD1 enrolled in the Gaucher Registry who received ERT and did not report AVN prior to starting therapy (n = 2700) were included. The incidence rate of AVN following initiation of ERT was determined. An incidence rate of AVN of 13.8 per 1000 person-years was observed in patients receiving ERT. Patients who initiated ERT within 2 years of diagnosis had an incidence rate of 8.1 per 1000 person-years; patients who started ERT >or=2 years after diagnosis had an incidence rate of 16.6 per 1000 person-years. The adjusted incidence rate ratio was 0.59 [95% confidence interval (CI) 0.36-0.96, P = 0.0343]. Splenectomy was an independent risk factor for AVN (adjusted incidence rate ratio 2.23, 95% CI 1.61-3.08, P < 0.0001). In conclusion, the risk of AVN was reduced among patients who initiated ERT within 2 years of diagnosis, compared to initiating treatment >or=2 years after diagnosis. A higher risk of AVN was observed among patients who had previously undergone splenectomy.