Context .- Sessile serrated adenomas/polyps (SSA/Ps) have been increasingly studied during the last 10 years. However, their detailed anatomic distribution pattern has not been studied, especially given newer (broader) criteria for the diagnosis. Objectives .- To characterize the anatomic distribution of SSA/P with and without cytologic dysplasia and to assess the demographics of these patients in a nationwide database. Design .- We retrospectively analyzed the database of Miraca Life Sciences Research Institute for a 1-year period. Patients with a diagnosis of SSA/P, SSA/P with low-grade cytologic dysplasia (SSA/P-LGD), SSA/P with high-grade cytologic dysplasia (SSA/P-HGD), or SSA/P with adenocarcinoma (SSA/P-ACA) were retrieved, and patients' age, sex, and specific anatomic location were analyzed. Results .- A total of 11 201 patients were identified, of which 10 646 (95.0%) had SSA/P, 514 (4.6%) had SSA/P-LGD, 39 (0.35%) had SSA/P-HGD, and 2 (0.018%) had SSA/P-ACA. All SSA/Ps and more advanced lesions were significantly more common in the proximal colon-SSA/P (61.2%), SSA/P-LGD (61.2%), SSA/P-HGD (80%), and SSA/P-ACA (100%)-than in either the transverse (18.8%, 17.8%, 10.0%, and 0%, respectively) or the distal (19.9%, 21.0%, 10.0%, and 0%, respectively) colon, P < .001. Sessile serrated adenoma/polyp with cytologic dysplasia was most commonly found in the ascending colon (LGD, 31.6%) and cecum (HGD, 37.5%). Advanced SSA/Ps were disproportionally more common among older women. Conclusions .- Sessile serrated adenomas/polyps with and without cytologic dysplasia and carcinoma are predominantly found in the cecum and ascending colon, whereas there is low prevalence in both the transverse and distal colon. Confirmation of previously published data regarding demographics of advanced lesions among a different cohort and including newer (broader) criteria suggests these criteria are valid.