Background: People with intellectual disability have poor balance skills and greater fall risk. The Short Physical Performance Battery (SPPB) provides comprehensive information on functional status and can predict fall risk. However, the reliability and validity of the SPPB have not been evaluated in people with intellectual disability. Methods: Seventy-eight adults with intellectual disability were assessed using the SPPB twice. Reliability was analysed with intraclass correlation coefficient and validity was assessed against the Timed Up & Go (TUG) test and the stabilometric test using Spearman's rho. Results: Reliability was moderate to high in all SPPB components except for the semi-tandem and full tandem positions. The SPPB summary score indicated moderate test-retest reliability and showed mostly significant moderate associations with the TUG and poor agreement with the stabilometric test. Conclusions: The SPPB summary score indicated high internal consistency, moderate reliability, and moderate validity when applied to adults with intellectual disability.