There has been an increased use of vitamin D both by prescription and by the public as a widely available supplement. We evaluated 15 years of single-substance vitamin D exposures to US poison centers. Methods: Retrospective analysis of data from the National Poison Data System (NPDS) to evaluate clinical effects, trends, and outcomes of exposures to vitamin D over the period January 1, 2000 through June 30, 2014. Cases were limited to exposures involving vitamin D as a single substance. Multiple vitamin products that may have included vitamin D were not included in this study. Results: From 2000 through June 30, 2014, there were 25,397 human exposures to vitamin D reported to NPDS. There was a mean of 196 cases per year from 2000 to 2005, followed by a 1600% increase in exposures between 2005 and 2011 to a new annual mean of 4535 exposures per year. The mean and median ages were 23.4 years and 10 years, respectively. There were no fatalities, but five (0.02%) major effect outcomes. Serious medical outcomes (major or moderate outcome) were infrequent, ranging from 2 patients/year to 22 patients/year. Clinical effects were primarily gastrointestinal (0.7–1.5%) and mild neurological effects (0.2–0.4%). There was a decline in the percentage of patients treated in a health care facility and of patients with serious medical outcome. Conclusion: Despite the enormous increase in number of exposures, there was not a significant increase in patients with a serious medical outcome. Rare severe outcomes may occur.