A healthy 13-year-old white boy presented with vomiting, diarrhea, and fatigue after a 3-day youth group project in a rural setting. Workup revealed a hemoglobin concentration of 9.9 g/dL (to convert to grams per liter, multiply by 10), mean corpuscular volume of 77 L, C-reactive protein of 26 mg/L (to convert to nanomoles per liter, multiply by 9.524), and a erythrocyte sedimentation rate of 50 mm/hour. The anemia did not respond to iron therapy. Over the course of 6 weeks, the patient lost 5.4 kg, developed photophobia, and became uncharacteristically sullen, angry, and combative. Funduscopic examination and fluorescein angiography revealed uveitis, interpreted as highly consistent with sarcoidosis (Figure 1). His serum angiotensin-converting enzyme level was 113 U/L (reference range, 12-68 U/L; to convert to nanokatals per liter, multiply by 16.667). Magnetic resonance imaging of the brain showed prominent periventricular and subcortical white matter changes (Figure 2A). The patient was treated with prednisone and methotrexate and improved in 1 year. Follow-up after 1 year showed significant resolution of uveitis and cerebral white matter lesions (Figure 2B).