Purpose: To evaluate the frequency and estimated costs of additional diagnostic workup for extracolonic findings detected at computed tomographic (CT) colonography in a large screening cohort. Materials and This retrospective HIPAA-compliant study, which had in- Methods: stitutional review board approval, evaluated extracolonic findings in 2195 consecutive asymptomatic adults (1199 women, 996 men; age range, 40-90 years; mean age, 58.0 years ± 8.1 [standard deviation]) undergoing low-dose CT colonographic screening performed without contrast material at a single institution over a 20-month period. All diagnostic workups generated because of extracolonic findings were reviewed. Associated costs were estimated by using 2006 Medicare average reimbursement. Testing for statistical significance was performed by using the φ 2 and t tests. Results: Further diagnostic workup for unsuspected extracolonic findings was performed in 133 (6.1%) of 2195 patients, including 18 patients in whom additional workup was not recommended by the radiologist. Additional testing included ultrasonography (n = 64), CT (n = 59), magnetic resonance imaging (n = 11), other diagnostic imaging tests (n = 19), nonsurgical invasive procedures (n = 19), and surgical procedures (n = 22). Benign findings were confirmed in the majority of cases, but relevant new diagnoses were made in 55 (2.5%) patients, including extracolonic malignancies in nine patients. The mean cost per patient for nonsurgical procedures was $31.02 (95% confidence interval: $23.72, $38.94); that for surgical procedures was $67.54 (95% confidence interval: $38.62, $101.55). Conclusion: Detection of relevant unsuspected extracolonic disease at CT colonographic screening is not rare, accounting for a relatively large percentage of cases in which additional workup was recommended. Judicious handling of potential extracolonic findings is warranted to balance the cost of additional workup against the potential for early detection of important disease, because many findings will prove to be of no clinical consequence.