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Introduction Asymptomatic physiological hypercalcaemia in exclusively breastfed infants is recognised but has not been systematically characterised when breastfeeding is continued.Objective To evaluate the clinical, biochemical and radiological outcomes of breast milk–associated physiological hypercalcaemia.Methods A multi-centre retrospective study over 5 years included infants with hypercalcaemia (serum corrected calcium (cCa) ≥2.8 mmol/L) who were exclusively breastfed and had no other identifiable causes of hypercalcaemia. Clinical, biochemical and radiological data were analysed.Results Twenty-five infants (15 males, 10 females) were studied. The mean peak cCa was 3.08 mmol/L (SD 0.17; normal 2.2–2.8 mmol/L). All infants were asymptomatic and continued exclusive breastfeeding without interventions such as intravenous fluids, diuretics or bisphosphonates. Mean serum parathyroid hormone (PTH) was suppressed at 1.04 pmol/L (SD 0.9; reference 2.0–9.4 pmol/L). Renal ultrasound examinations performed in all infants showed no nephrocalcinosis. Hypercalcaemia resolved spontaneously over a median of 64 (range, 9–329) days, and the median duration of exclusive breastfeeding was 150 (range, 8–540) days.Conclusion Breast milk–associated physiological hypercalcaemia is a benign, PTH-independent condition without clinical symptoms or nephrocalcinosis. Infants can safely continue exclusive breastfeeding, preserving its well-established benefits, without switching to low calcium formulas. Further research is needed to elucidate the underlying mechanisms.