Isolated cleft lip and/or palate, CL(P), may be associated with multiple changes in the developing dentition. To test the hypothesis that permanent tooth formation is delayed in patients with CL(P), dental maturity was assessed from panoramic radiographs. The dental maturity ratio (DMR, dental age divided by chronological age) of a group of CL(P) patients (23 girls, 30 boys) was compared with matched control subjects (38 girls, 41 boys). The mean DMR in cleft boys (0.97 +/- 0.01) was significantly lower than in control boys (1.06 +/- 0.01), P < 0.05. The mean DMR in cleft boys was lower than in cleft girls (1.02 +/- 0.02), with a tendency toward statistical significance. No significant difference in DMR was found between the cleft versus control girls, or between the control girls and boys. Among cleft boys, the prevalence of dental age delay was 67% (20/30), with a mean delay of 0.6 +/- 0.4 years. These results suggested that CL(P) may be associated with delay in permanent tooth formation.