Background: The aim of this study was to evaluate the prevalence and computed tomography (CT) appearances of accessory spleens in hospital-based patients, and to measure and make comparisons between accessory spleen size and density. Methods: A cross-sectional study was carried out in a diagnostic center in Erbil, Iraq during January–December, 2012. Biphasic abdominal CT images of 334 consecutive patients with different age groups were evaluated for the presence of an accessory spleen, and if identified, it was further analysed for shape, diameter, density, number, and location. Patients with inadequate CT techniques, splenectomy, hematological disorders, and widespread lesions in the abdomen were excluded from this study. Results: Of the 334 patients (198 female, 136 male), with a mean age of 47.2 years (SD 15.7), 82 accessory spleens were detected in 63 patients (18.8%). Their mean diameter was 14.7 mm (range 3–79 mm), 68% were round in shape and 75.6% were medial to the main spleen. Sixty percent of the cases showed a single accessory spleen and 40% had more than one (up to 4 detected). A significant difference in the mean diameter of accessory spleens between similar and different densities than the main spleen was observed (P = 0.018), 71 accessory spleens (mean diameter = 15.97 mm) displayed similar densities to the main spleen, while 11 (mean diameter = 7.09 mm) were hypodense or hyperdense to the main spleen. Conclusions: The prevalence of an accessory spleen is high, and should be considered by radiologists during abdominal CT scan reporting.