The purpose of this study was to evaluate the impact of computed tomography coronary angiography (CTCA) on the appropriate utilization of catheter angiography (CA). This observational trial analyzed all patients undergoing CA in 2006 and 2007 in one hospital. In 2007, patients having a low to intermediate cardiovascular risk and suspicion of coronary artery disease (CAD) and those with suspicion of progression of known organic heart disease (OHD) underwent CTCA either prior to CA or as the sole imaging modality. Appropriate utilization of CA was defined as: (1) percentage of patients showing normal or non-significant findings at CA, (2) percentage of self-referred patients to CA, and (3) percentage of patients with known OHD undergoing CA without immediate operative or interventional consequences. Use of CTCA resulted in a significant drop in the percentage of CA examinations in patients with suspected CAD showing normal or non-significant findings (19% in 2006, 10% in 2007, P < 0.001). The percentage of self-referred CA significantly dropped (29% in 2006, 10% in 2007, P < 0.001). CT ruled-out CAD in 74/151 (49%) patients, obviating subsequent CA. During a follow-up of 15 ± 4 months, CA and percutaneous interventions was considered necessary in 2/74 patients. CT ruled-out progression of known OHD in 53/60 (90%) patients, while one patient underwent CA and percutaneous intervention during a follow-up period of 16 ± 4 months. No reduction of CA examinations without immediate consequences was found in patients with known OHD (13% in 2006, 27% in 2007). In patients with suspicion of CAD, CTCA improved the appropriate utilization of CA without jeopardizing patient safety, along with a decrease of self-referred patients for CA. CTCA did not influence the appropriate utilization of CA in patients with known OHD.