This study compared oral health behaviours and barriers to dental care among preschool children with and without ASD, and evaluated dental knowledge and attitudes of their parents. 257 preschoolers with ASD and an age- and gender-matched control sample were recruited. Children with ASD had less frequently performed tooth-brushing and used toothpaste, but more often required parental assistance in tooth-brushing (p < 0.05). Barriers to dental care were more frequently reported among children with ASD (p < 0.001). Parents of children with ASD had higher scores in dental knowledge and attitudes than those without ASD. Differences in oral health behaviours and barriers to dental care existed between preschool children with and without ASD. Parents of children with ASD had better dental knowledge and attitudes.