In 1979, 96 patients who had undergone hemodialysis for a mean of 3 years and 4 months were entered into this study. This follow-up study revealed that the bilateral kidney volume significantly increased over 10 years in 33 male patients. Kidneys were found to have enlarged 2.7 times over the 10-year follow-up period. However, in 24 females kidney volume did not change over 10 years. This paper reports further results in 39 dialysis patients (21 males and 18 females) who were followed from the 10th to 15th year. In male patients, mean volume was 196 +/- 218 ml (mean +/- SD) at the 10th year and had significantly increased to 225 +/- 213 ml at the 15th year (p < 0.02). In female patients, mean kidney volume was 78 +/- 51 ml at the 10th year and had increased to 117 +/- 91 ml at the 15th year (p < 0.01). The enlargement in kidney volume during the recent 5 years was 1.26 +/- 0.39-fold in males and 1.43 +/- 0.45-fold in females. These rates did not significantly differ between males and females. During this recent 5-year period, there were no surgical cases due to renal cell carcinoma. Therefore, over the entire patient-time dialysis period, there were 6 renal cell carcinomas in 1,470 patient years. In conclusion, 10- to 15-year follow-up studies of kidney size revealed that the enlargement in the kidney due to acquired cysts persisted in male patients, but the rate of increase slowed after 13.0 years of hemodialysis, while the enlargement in the kidney in female patients became significant at 17.7 years of hemodialysis, revealing the slowly progressive nature of acquired cysts in women.