A simple, specific method is described for the determination of creatinine in urine by HPLC. A C18-reversed-phase column is used for the separation. Detection is with a spectral UV-absorption photometer at 235 nm. The results for the precision and the accuracy meet the guidelines of the statistical quality control. Comparative investigations using the method by Lim et al. ((1978), J. Chromatogr. 67, 182-187) matched well with a coefficient of reference of 0.994. The specificity of the method was confirmed by the UV-absorption spectrum of creatinine isolated by HPLC. In addition, 28 urinary constituents were tested for possible interference.