A case series of 78 term infants with an ionized calcium of less than 1 mmol per liter found that their median age was eight days, and they consisted of disproportionately more males and Hispanic babies. Most presented with seizure-like activity. Most of them had high phosphate levels, low magnesium levels, and low or inappropriately normal parathyroid hormone levels. Among 42 infants in whom 25-hydroxy vitamin D levels were checked, 35 had levels less than 20 ng/mL. All infants responded within a short duration to treatment with one or more of the following: calcium supplements, calcitriol, low phosphorus formula, and magnesium supplementation. Neuroimaging generally yielded few significant findings.