PURPOSE: To measure and compare hand function for children with normal hand development, congenital hand differences (CHD), and neuromuscular disease (NMD) using a function test with touch screen technology designed as an iPhone application. METHODS: We measured touch screen hand function in 201 children including 113 with normal hand formation, 43 with CHD, and 45 with NMD. The touch screen test was developed on the iOS platform using an Apple iPhone 4. We measured 4 tasks: touching dots on a 3 × 4 grid, dragging shapes, use of the touch screen camera, and typing a line of text. The test takes 60 to 120 seconds and includes a pretest to familiarize the subject with the format. Each task is timed independently and the overall time is recorded. RESULTS: Children with normal hand development took less time to complete all 4 subtests with increasing age. When comparing children with normal hand development with those with CHD or NMD, in children aged less than 5 years we saw minimal differences; those aged 5 to 6 years with CHD took significantly longer total time; those aged 7 to 8 years with NMD took significantly longer total time; those aged 9 to 11 years with CHD took significantly longer total time; and those aged 12 years and older with NMD took significantly longer total time. CONCLUSIONS: Touch screen technology has becoming increasingly relevant to hand function in modern society. This study provides standardized age norms and shows that our test discriminates between normal hand development and that in children with CHD or NMD. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic III.