Cemented total knee arthroplasty for gonarthrosis in patients 55 years old or younger. The results of 68 cemented total knee arthroplasties (TKAs) in 50 patients with gonarthrosis who were 55 years old or younger at the time of surgery were reviewed. These patients were operated on between 1979 and 1987 and were followed for an average of 6.2 years. The average age of the patients was 50 years. Patients were evaluated by the Hospital for Special Surgery knee score. The average preoperative score was 53, and the average follow-up score was 90. Overall, 55 TKAs were rated as excellent and 13 as good. Using the knee rating score advocated by the Knee Society, the average postoperative score was 92 for pain and 84 for function. There were four successful reoperations for patellar component loosening, all in metal-backed patellae. The femoral and tibial components in these patients were intact, and at the follow-up period, two knees were rated as excellent and two as good. Detailed roentgenographic evaluation demonstrated that 20% of tibial components had radiolucencies in at least one zone on the anteroposterior roentgenogram and in 11% on the lateral roentgenogram. Femoral radiolucencies occurred in only 2% of knees. Patellar radiolucencies in one or more zones occurred in 20% of knees that had not had patellar revision. No complete or progressive radiolucencies at the bone-cement interface were noted for any component, and no components were considered to be roentgenographically loose. Cemented TKAs can achieve excellent long-term results in patients younger than 55 years old with gonarthrosis of the knee. These results compare with those obtained in published reports on older age groups. 