The use of color Doppler sonography to evaluate the symptomatic testes in children with scrotal pain or swelling was prospectively studied with a fourth-generation color sonographic unit with a 7-MHz linear transducer. The 32 patients were 1 day to 18 years old (mean age, 8.6 years). Results were correlated with scintigraphic findings in 23 patients, with the final diagnosis established by surgery in 12 patients, and with clinical follow-up in all patients. Eight cases of testicular torsion, including two of acute torsion and six of late torsion, were correctly detected by color Doppler sonography and confirmed surgically. In the remaining patients, perfusion of the testis was correctly detected by color Doppler examination. The final diagnoses in these patients included torsion of the appendix testis (15 patients), epididymitis (five patients), epididymo-orchitis (one patient), yolk sac tumor of the testis (one patient), hydrocele (one patient), and local reaction to an insect bite (one patient). The ability to detect blood flow in the normal contralateral testis was also evaluated in 28 patients. Blood flow was demonstrated in normal testes larger than 1 cm3. Detection of flow in the very small normal prepubertal testis was often difficult, and no flow was identified in one testis. Flow was identified in central arteries in only six of 13 testes smaller than 1 cm3. We conclude that color Doppler sonography is helpful in the initial evaluation of pediatric testes, providing accurate evaluation of the involved hemi-scrotum in our patients and also providing the benefit of both structural and flow information. Until our sensitivity to low-velocity flow improves, we would not suggest the exclusive use of color Doppler sonography in the evaluation of testicular perfusion in the prepubertal patient. We advocate the addition of testicular scintigraphy to corroborate the presence of testicular perfusion when flow in intratesticular arteries cannot be established with certainty by color Doppler sonography.