Individuals with sickle cell disease (SCD) have historically been considered underweight. Despite increasing body mass index (BMI) in the general population, the prevalence of overweight and obese status remains unclear in the adult SCD population. Our primary aim was to determine the prevalence of overweight and obese status and to identify associations between BMI, demographic, and clinical characteristics. We conducted an analysis of abstracted electronic health record data and patient-reported outcomes from the Sickle Cell Disease Implementation Consortium registry; individuals aged 20-45 years were included. The median (interquartile range) BMI for the 1664 adults in this analysis was 23.9 (21.1-28) kg/m2 . In this cohort, 42.9% had a BMI of >25 kg/m2 (Centers for Disease Control and Prevention definition of overweight/obese). In multivariable analysis, higher odds of being overweight or obese were associated with female gender, older age, college education, private insurance, and hypertension diagnosis. Higher odds of a BMI of >25 kg/m2 were observed in individuals with HbSC or HbSβ+ thalassaemia regardless of hydroxycarbamide (hydroxyurea) exposure (odds ratio [OR] 3.4, p < 0.0001) and HbSS or HbSβ0 thalassaemia exposed to hydroxycarbamide (OR 1.6, p = 0.0003) compared to those with HbSS or HbSβ0 thalassaemia with no hydroxycarbamide exposure. These data highlight the importance of early identification, prevention, and intervention for increasing BMI to reduce obesity-related complications that may impact SCD-related complications.