To identify modifications of kidney morphology and of the time-velocity spectral waveform associated with long-term compensatory hypertrophy, spectral Doppler sonography was performed in 30 children and adults with solitary kidneys 7 years to 28 years following nephrectomy. Doppler signals were obtained from three arterial sites in each kidney. The average renal volume was 207 mL and the mean hypertrophy of the kidneys was 186%. The mean value of pulsatility (PI) and Pourcelot (RI) indexes of solitary hypertrophied kidneys was significantly lower than that of normal paired kidneys or allografts with normal function described in the literature. The PI and RI were found to correlate inversely with the kidney volume and the body surface area (BSA). In spite of a long follow-up time, no patient suffered from renal failure. This study suggests that in the case of solitary kidney, specific ranges of PI and RI should be employed rather than those used with paired kidneys.