Objective: To develop a normogram for upper arm measurements for the evaluation of exclusively breastfed infants and to evaluate the clinical usefulness of the normogram. Design: A prospective study involving the evaluation of infants discharged from the Newborn Unit and follow-up for the first six months of life while being exclusively breastfed, Setting: Neonatal follow up Clinic, University Teaching Hospital, Benin City, Nigeria from 1st June, 1995 to 31st May, 1997, Subjects: A total of 219 exclusively breastfed infants were recruited and analysed for the development of the normogram, A second group of 100 normal exclusively breastfed infants were evaluated to determine the clinical usefulness of the normogram, Interventions: Determination of the upper arm measurement of the infants and development of the normogram using the statistics of the regression analysis of these measurements on postnatal age. Main outcome measures: Upper arm measurements, mean measurements at each completed month, regression statistics (MAC on postnatal age). Results: Mean MAC measurements increased progressively from the first to the sixth completed months. There was a significant difference between the mean measurements at the 4th and 6th completed months. Upper arm measurements showed a highly significant correlation with postnatal age and the regression line and the 95% confidence limits were used to develop the normogram, Of the 100 infants in the second group, 92% had normal infant growth using the normogram, Conclusion: The developed normogram of upper arm measurements was evaluated to be clinically useful in exclusively breastfed infants.