At this time, there is evidence that PALS, like those with other chronic illnesses, are at increased risk for vitamin D deficiency. It is, therefore, reasonable to screen PALS for this. If vitamin D deficiency is found, it seems reasonable to supplement vitamin D according to established guidelines (31) in order to avoid medical complications of vitamin D deficiency. It is not yet clear, however, that vitamin D supplementation can slow disease progression, improve muscle strength, or reduce falls in PALS. We support further studies to answer these questions.