Three exclusively breastfed term neonates were admitted with lethargy, poor feeding, and oligoanuria. All three babies were severely dehydrated and had a weight loss ranging from 18% to 40%. Serum sodium of more than 180 mEq/l and renal failure were observed in all three. Two had very high creatinine levels of 9.5 mg/dl and 6.7 mg/dl. Both these babies also had multiple seizures. One baby required mechanical ventilation. All three babies showed markedly hyperechoic renal medullary pyramids with speckled foci suggestive of crystal deposition that reversed completely on therapy. Urine showed abundant urate crystals in two and an elevated calcium/creatinine ratio of 1.6 in one. There was no evidence of distal renal tubular acidosis, Bartter syndrome, or high serum calcium. Supersaturation of the ions in a markedly hypertonic renal medulla may have led to crystallization, with resolubilization with hydration and restoration of good urine output. The hypernatremic dehydration was primarily due to lactation failure leading to inadequate fluid intake in the face of ongoing insensible losses. High breast milk sodium may have been a contributory factor in one patient.