No studies have examined the association between body habitus and incidence of pituitary adenoma.To determine if body mass index (BMI), waist circumference, body somatotype, or height are associated with risk of pituitary adenoma.Pooled analysis of three prospective cohort studies.Population-based study.Participants of the NHS, NHSII, and HPFS, totaling 284,946 American health professionals.BMI, waist circumference, body somatotype, and height.Self-reported incident pituitary adenoma. Multivariable (MV)-adjusted hazard ratios of pituitary adenoma were estimated using Cox proportional hazards models.During 7,350,156 person-years of follow up, 387 incident pituitary adenomas were reported. Comparing BMI of ≥30 to <25 kg/m 2, higher adult BMI was associated with higher risk of pituitary adenoma (MV HR=1.74, 95%CI:1.33-2.28), as was higher maximum adult BMI (MV HR=1.76, 95%CI:1.34-2.30), higher waist circumference (MV HR=1.06, 95%CI: 1.04-1.09 per inch), and higher BMI during early adulthood (at age 18-21, MV HR=2.65, 95%CI:1.56-4.49). Taller adult height was associated with pituitary adenoma (MV HR=1.05, 95%CI:1.01-1.09 per inch). Overall findings were similar in women and men, although power was limited in men (n=62 cases). Sensitivity analyses demonstrated that the association between adult BMI and pituitary adenoma extended to at least 14 years prior to diagnosis and that the results were not affected when analyses were restricted to participants with similar healthcare utilization.Higher BMI and waist circumference, from early adulthood to the time of diagnosis, were associated with higher risk of pituitary adenoma.