Gaucher disease (GD) is a lysosomal storage disorder characterized by anemia and thrombocytopenia, hepatosplenomegaly, and skeletal involvement. The management of Gaucher disease was improved by the development of enzyme replacement therapy (ERT). However, the bone response to ERT is generally slower compared to other clinical manifestations. Some have recommended the early use of ERT to prevent the development of severe skeletal complications. Because we have access to over 30 untreated patients in Ontario, we questioned the extent to which complications progress in severity over a long period of time. We examined retrospectively the natural history of GD and the extent of skeletal manifestations in 22 untreated type 1 GD adult patients (mean age, 49+/-3.3; range, 20-81 years). The patients were followed for a median of 9.5 years (range, 3-16 years). Hemoglobin (Hb) concentration did not significantly change over time (mean baseline concentration of 12.8+/-0.27 g/dL vs. mean recent concentration of 12.6+/-0.37 g/dL, p=0.65). Mean platelet count also remained relatively stable over time (mean baseline count of 138+/-13x10(9)/L vs. mean recent count of 138.5+/-18x10(9)/L, p=0.98). Mean ferritin and ACE concentrations were elevated and were stable over time. Liver volumes decreased over time (mean baseline liver volume of 1.2xnormal (N) vs. mean recent volume of 1.06xN, p=0.27) and 6 of 22 (27%) patients had moderate hepatomegaly (liver volume, 1.25-2.5xN). Spleen volumes remained stable over time (mean baseline spleen volume of 6.6xN vs. mean recent volume of 5.2xN, p=0.5). None of the changes was statistically significant. Four of 20 (20%) patients had moderate splenomegaly (spleen volume, 5-15xN), 2 of 20 (10%) had marked splenomegaly (spleen volume, >or=15xN), and 2 of 22 (9%) had had splenectomy. The most common skeletal manifestations were infiltration of the bone marrow in 16 of 22 (73%) patients followed by osteopenia in 15 of 22 (68%), Erlenmeyer flask deformity in 13 of 22 (59%), and infarctions in 6 of 22 (27%) patients. We observed that bone disease remained relatively stable over time in most patients, although three patients developed new infarcts over time, one developed an avascular necrosis (AVN), and four had an increase in the degree of osteopenia. Although GD and its skeletal complications progress in severity in some patients, our results suggest that GD complications, including bony disease, may stabilize over time. Therefore, early use of ERT may not be necessary in all type 1 GD patients.