We estimated the number of patients with chronic renal failure (CRF) but not with end-stage renal disease (ESRD) in Japan by two methods: a nationwide survey and an estimation using incidence rates of ESRD among CRF patients as well as the number of incident ESRD. The former estimated the number of patients with CRF but not with ESRD as 154,000 (95% confidence interval 139,000-168,000), while so did the latter as 142,000 (133,000-150,000). It follows that the number of CRF patients including ESRD could amount to more than 300,000, which would give a substantial impact on public health in Japan. Despite some own methodological issues in estimation, the two estimates were reasonably in good agreement: supporting their methodological validity in estimation, since sources of errors appeared to be quite independent of each other.