Recent studies provide evidence that the Restricted, Repetitive Behaviours, and Interests (RRBI) domain of autism is heterogeneous, consisting of at least two factors: Insistence on Sameness (IS) and Repetitive Sensory and Motor Behaviours and Interests (RSMB) [Cuccaro et al. ("Child Psychiatry and Human Development," 34, 3-7, 2003; Szatmari et al. ("Journal of Child Psychology and Psychiatry," 47, 582-590, 2006)]. The main objective of this study was to replicate this two-factor structure in an independent sample of 153 Greek individuals with a diagnosis of Pervasive Developmental Disorder (PDD). Principal Component Analysis was used to analyze the data. Our findings confirmed the two-factor structure (accounting for 52% of the variance), providing evidence for the cross-cultural heterogeneity of the RRBI domain of autism and the clear distinction between IS and RSMB symptoms in individuals with PDD.