Previous studies have established normal penile length for patient age and stage of sexual development. To our knowledge penile length has only been determined to date by measuring the stretched distance from the symphysis to the glans tip. Pilot studies at our institution showed that ultrasound corpora cavernosa length determinations were possible using a 7.5 MHz. linear transducer probe. To determine whether ultrasound is a more accurate modality in assessing penile length, male subjects 0 to 24 months old with normal penile anatomy and palpably descended testicles were enrolled in a prospective analysis. Longitudinal ultrasound images of the flaccid penis were obtained from the dorsal surface. The whole corporeal bodies were easily imaged and measured. In a blinded fashion a separate investigator performed a conventional stretched penile length determination. A total of 27 male subjects 1 week to 22 months old was evaluated and 2 were excluded. Corpora cavernosa measurements using ultrasound revealed a mean length of 32.3 +/- 4.7 mm. (range 22.4 to 44.9). Stretched penile lengths of the same subjects revealed a mean length of 46.8 +/- 8.2 mm. (range 31 to 63). Circumcision status (p = 0.036) and age (p < 0.001) significantly correlated with stretched length determinations. Ultrasound measurements did not significantly vary with patient circumcision status or age. Penile length and race were not correlated when using stretched or ultrasound measurements. Ultrasound determination of corporeal body length is possible in young subjects. From infancy to age 22 months ultrasound measurements are not significantly affected by age or the presence of foreskin. Our experience suggests that corporeal body evaluation by ultrasound may offer a more accurate assessment of functional penile length.