Objectives: To determine the gestational weight gain (GWG) percentiles according to pregestational body mass index (BMI) and birth weight at Honorio Delgado Hospital of Arequipa. Design: Descriptive observational study. Institution: Hospital III Honorio Delgado of Arequipa, Peru. Participants: Healthy pregnant women between 37 and 41 weeks of gestation who came to the hospital from July 2015 to June 2016 for delivery. Methods: Selection by systematic randomization of 1 007 pregnant women. Main outcome measures: The mean and percentiles of the total GWG were determined quarterly, monthly and weekly. Results: The 1 007 pregnant women had a mean maternal age of 26.7 years, a pregestational BMI of 25.7 and the average newborn weight was 3 456 g. According to the birth weight ranging from 2 780 to 3 820 g, the 25th and 75th percentile of the total GWG were 8.1 to 13.3 and 9.0 to 13.9 for low ...