Play is an essential component of children's development. Children with intellectual disability tend to have poor socioemotional abilities and impaired play. This study examined the effects of a medical/therapeutic clowning play intervention on the playfulness of children with intellectual disability. Two medical clowns facilitated a play intervention in a preschool classroom setting with a total of 52 children with intellectual disability. We compared before and after two groups that received the intervention: group 1 met the medical clowns once a week for 6 months (long-intervention group) and group 2 for 3 months (short intervention group). Children's functioning was assessed using the Vineland Adaptive Behaviour Scales. Children's playfulness was scored using the Test of Playfulness observational assessment. A teachers' focus- group was used to gather additional information on the clowns' work. Children's playfulness increased significantly at the end of the intervention, whereas the improvement in the playfulness scores of group 1 was significantly larger than those of group 2 (t50 = -4.82, p< .001). The teachers' focus group revealed additional benefits of the medical clowns' work. The results shed light on the play and playfulness of children with intellectual disability and the possible contribution of a clowning play intervention to their development.