A 57-year-old woman presented to the hospital after a 40-day acaloric (water-only) fast, which was motivated by her Christian beliefs and Pentecostal affiliation. She exhibited hyponatremia on admission, and developed hypokalemia, hypophosphatemia and hypomagnesemia during refeeding. The authors are unaware of other published case reports describing medical and religious aspects of prolonged fasting by Christians for spiritual reasons. Nevertheless, this practice is advocated by some Pentecostal and non-Pentecostal sources, and may be more common than is widely recognized.