OBJECTIVE: Determination of long-term results of hip replacements in patients who, at the time of operation, were under the age of 50. Procedures whereby an existing acetabulum defect was filled with bone chips that were impacted into a strong layer, after which a cemented total hip prosthesis was implanted. DESIGN: Descriptive. METHOD: Prospectively collected data from patients who were under the age of 50, and had undergone a hip replacement operation at our hospital between 1 July 1979 and 31 December 1987 were analysed. Data were collected up to 31 December 2002. The main outcome was time to revision. Survival was calculated by the Kaplan-Meier method. RESULTS: The study group consisted of 25 patients, 17 women and 8 men with 29 prosthetic hips. The average age at operation was 37.6 years (range: 20-49). Follow-up time was 15-23 years (median: 18.7 years). 1 patient (1 hip) was lost to follow-up. 3 patients (4 hips) died within 15 years after the operation; none of them had undergone revision. 4 revisions had been performed: I septic loosening (14 years p.o.) and 3 aseptic loosenings (6, 15, 20 years p.o.). The cumulative survival with the end-point 'revision for any reason' was 96% (95% CI: 88-100) at to years and 88% (95% CI: 74-100) at 20 years; after exclusion of the septic loosening the survival at 20 years was 92% (95% CI: 80-100). CONCLUSION: Hip replacement including a reconstruction technique for an acetabulum defect in patients under the age of 50 was regarded as successful if after 10 years, at least 90% of the prostheses were still in situ