BACKGROUND AND OBJECTIVE: Accurate data on the optimal chloride (Cl) intake in premature infants are scarce. The aim of the present study was to describe Cl intakes in the first 10 days of life and to assess the relations between high Cl intakes and corrected serum Cl level or markers of severe acidosis in infants \textless28 weeks' gestation. METHODS: Retrospective cohort study including all of the infants \textless28 weeks admitted to the neonatal intensive care unit during a 3-year period and cared for from birth until day 10 or more. RESULTS: Fifty-six infants were included. Cumulative total Cl intakes reached 9.6 ± 3.7 mmol/kg at day 3 and 49.2 ± 13.5 mmol/kg at day 10. Inadvertent intakes (from intravenous fluids other than parenteral nutrition) represented on average 70% of total Cl intakes in the first 3 days. Difference between Cl and sodium intakes reached 7.8 ± 4.8 mmol/kg at day 10 and mainly originated from parenteral nutrition. By multivariate analysis, cumulative Cl intake \textgreater10 mmol/kg during the first 3 days was an independent risk factor of base excess \textless-10 mmol/L. Cumulative Cl intake \textgreater45 mmol/kg during the first 10 days was an independent risk factor of corrected chloremia \textgreater115 mmol/L and of base excess \textless-10 mmol/L. CONCLUSIONS: Cumulative Cl intake \textgreater10 mmol/kg during the first 3 days (ie, 3.3 mmol · kg (-1) · day(-1) on average) and \textgreater45 mmol/kg during the first 10 days (ie, 4.5 mmol · kg (-1) · day(-1) on average) may have unwanted metabolic consequences and should be avoided. Imbalance between electrolytes provided by the parenteral nutrition solution need to be detected and corrected.