Objective A marked decrease in the density of interstitial cells of Cajal (ICC) has been shown in patients with ureteropelvic junction obstruction. ICC may also play a role in primary obstructive megaureter (POM). An immunohistochemical study was conducted to investigate the density of ICC in ureterovesical junction (UVJ) segments resected from patients with POM and from control autopsy specimens. Materials and methods Resected UVJ segments from 11 patients operated for POM comprised the study group. Control UVJs were obtained from autopsy specimens of 7 children who died from causes other than urogenital pathology. The UVJs including the narrowest parts were studied using immunohistochemical staining for C-kit positive cells. Results The number of ICC was significantly lower in the UVJs of the POM compared to the control group. The UVJs of the POM group had 1.75 ± 1.14 ICC (mean ± 1SD), whereas the control group had 5.76 ± 2.99 ICC (mean ± 1SD). Conclusion The number of ICC was decreased in the UVJs of the patients with POM compared to the normal control group. As dilation of the ureter during fetal life is a common condition and ureteral dilation is often self limiting, we hypothesize that ureteral peristalsis is a maturational event including the maturational development of ICC.