Across the United States, physicians are prescribing patients nature. These "Nature Rx" programs promote outdoor activity as a measure to combat health epidemics stemming from sedentary lifestyles. Despite the apparent novelty of nature prescription programs, they are not new. Rather, they are a reemergence of nature-based therapeutics that characterized children's health programs in the late 19th and early 20th centuries. These historic programs were popular among working-class urban families, physicians, and public health officials. By contrast, adherence is a challenge for contemporary programs, especially in socially disadvantaged areas. Although there are differences in nature prescription programs and social context, historical antecedents provide important lessons about the need to provide accessible resources and build on existing social networks. They also show that nature-and its related health benefits-does not easily yield itself to precise scientific measurements or outcomes. Recognizing these constraints may be critical to nature prescription programs' continued success and support from the medical profession.