Objectives: Adipose tissue affects several aspects of the cellular immune system, but prior epidemiological studies have differed on whether a higher body mass index (BMI) promotes CD4 T-cell recovery on antiretroviral therapy (ART). The objective of this analysis was to assess the relationship between BMI at ART initiation and early changes in CD4 T-cell count. Methods: We used the North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD) data set to analyse the relationship between pre-treatment BMI and 12-month CD4 T-cell recovery among adults who started ART between 1998 and 2010 and maintained HIV-1 RNA levels <400 copies/mL for at least 6 months. Multivariable regression models were adjusted for age, race, sex, baseline CD4 count and HIV RNA level, year of ART initiation, ART regimen and clinical site. Results: A total of 8381 participants from 13 cohorts contributed data; 85% were male, 52% were nonwhite, 32% were overweight (BMI 25-29.9kg/m2) and 15% were obese (BMI >30kg/m2). Pretreatment BMI was associated with 12-month CD4 T-cell change (P<0.001), but the relationship was nonlinear (P<0.001). Compared with a reference of 22kg/m2, a BMI of 30kg/m2 was associated with a 36cells/μL [95% confidence interval (CI) 14, 59cells/μL] greater CD4 T-cell count recovery among women and a 19cells/μL (95% CI 9, 30cells/μL) greater recovery among men at 12 months. At a BMI>30kg/m2, the observed benefit was attenuated among men to a greater degree than among women, although this difference was not statistically significant. Conclusions: A BMI of approximately 30kg/m2 at ART initiation was associated with greater CD4 T-cell recovery at 12 months compared with higher or lower BMI values, suggesting that body composition may affect peripheral CD4 T-cell recovery.