PURPOSE: The aim of this article was to determine reliability of the Test of Infant Motor Performance (TIMP) in infants with spinal muscular atrophy, type I (SMA-I). METHODS: Interrater reliability training was undertaken by 17 physical therapist evaluators using 6 infants with hypotonia and weakness (5 videotaped, 1 live). Eight trained evaluators then conducted a test-retest reliability study at their own center, performing 2 tests approximately 1 month apart on each of 11 infants with genetically confirmed SMA-I (5 boys, 6 girls; age range 37-501 days; 3 on pulmonary support). RESULTS: The interrater reliability training session had an overall weighted Kappa of 0.61 (95% confidence interval 0.59-0.63). For the test-retest reliability study, the intraclass correlation coefficient for the TIMP Total Score was 0.85 (95% confidence interval: 0.54-0.96). The test scores were not significantly different between the 2 sessions (Bradley-Blackwood test was nonsignificant). CONCLUSION: TIMP scores can be reliably obtained in infants with SMA-I.