Our goals were (1) to quantify protrusio acetabuli in patients with Marfan syndrome who underwent total hip arthroplasty and (2) to identify clinical results and complications associated with total hip arthroplasty in those patients. We reviewed the preoperative radiographs of the 29 patients (38 hips) in our study and analyzed the related patient operative reports, postoperative records, and self-administered questionnaires (mean follow-up, 116 ± 102 months). The mean preoperative center-edge angle of Wiberg was 50.9° ± 14°. Loosening (3) and radiolucent lines (4) occurred in femoral but not acetabular components. The hips had 15 complications, including 8 reoperations. High questionnaire scores (82 ± 13 points) indicated good hip function regardless of preoperative protrusio severity.