OBJECTIVE To monitor long-term pegvisomant treatment of patients with acromegaly in routine clinical practice. METHODS The French ACROSTUDY is part of the global ACROSTUDY, an observational post-authorization safety surveillance study of acromegaly treatment with pegvisomant. RESULTS The median duration of follow-up of the 292 included patients was 5.2 years. Overall 272 (93%) patients received somatostatin analogues before initiation of pegvisomant. The most prescribed initial dose of pegvisomant (after possible administration of a loading dose) was 10mg/day and, starting from the 2nd year, the median dose was 20mg/day. Serum IGF-1 concentration decreased as soon as pegvisomant was started and after 5 years there was a 62% mean decrease in serum IGF-1 concentration. The percentage of patients with serum IGF-1 concentration within normal ranges (for age and sex) of the local laboratory shifted from 11% at start of pegvisomant to 43% at 6 months and 63% after 5 years. The last available imaging (242 patients) showed an increased or decreased tumor size in 4 and 10% of patients, respectively. Mean weight increased by 3 kg over the 5-year period (P<10(-3)). Mean fasting blood glucose significantly decreased over time (P<0.05), while HbA1c level remained unchanged. Tolerance profile was generally good and similar to that described in clinical studies. CONCLUSIONS This analysis showed a significant decrease in IGF-1 levels throughout the follow-up period, and confirmed that pegvisomant treatment is safe in acromegaly. The results of this interim analysis remain to be confirmed by the final analysis.