We examined the characteristics of mastoid pneumatization in the Pierre-Robin syndrome (PRS) and non-PRS cleft palate population in relation to age. There were 14 patients with PRS (median age, 5 years), 7 patients with bilateral cleft lip-palates (BCLP: median age, 6 years), 29 patients with unilateral cleft lip-palates (UCLP: median age, 6 years) and 15 patients with isolated cleft palates (ICP: median age, 7 years). All had secretory otitis and ventilation tubes inserted. Pneumatization was assessed by standard computerized planimetric methods. Temporal bone (Schüller view) X-rays were obtained. Areas of bone pneumatization were outlined and measured separately for each ear. The median pneumatized area of the mastoid (MBP) in PRS patients (6.73 cm2) was significantly lower than in non-PRS cleft patients (7.29 cm2). It was also lower than in UCLP (7.35 cm2; P = 0.01) and ICP (7.19 cm2; P = 0.02). MBP did not change significantly with age in PRS (Spearman rs = 0.11) and BCLP (Spearman rs = 0.11), but did increase significantly in the ICP group (Spearman rs = 0.23; P = 0.04). Cubic regression showed the best fit in the BCLP (r2 = 0.61; P = 0.01) and ICP (r2 = 0.10; P = 0.05). It was not significant for PRS (r2 = 0.132) or UCLP (r2 = 0.049). We concluded that pneumatization in all cases increases with age, but it is statistically significant only in ICP. PRS patients have a lower area of mastoid air-cell size than the non-PRS cleft palate population. The extent of mastoid pneumatization in PRS patients does not correlate with age because of the negative influence of the mandibular hypoplasia and glossoptosis present.