The aim of this study was to investigate whether there was an association between presence of a cleft and reduced size of deciduous tooth on the cleft side. In this investigation, 58 study models of patients with unilateral cleft lip and palate with deciduous dentition were analyzed. The largest mesiodistal dimension of deciduous teeth was measured by a sliding caliper. The size of the same teeth on the side of the cleft and on the non-cleft side was compared. The results of the investigation were statistically analyzed. A difference between the genders was found. In the sample of boys the lateral deciduous incisor and the second deciduous molars on the cleft side were smaller than those on the non-cleft side, while in girls the central and lateral deciduous incisors were smaller on the cleft side than on the non-cleft side. It was concluded that the presence of a unilateral cleft lip and palate was associated with smaller tooth size.