To investigate and compare the dosimetric distribution of a conventional radiotherapy (CRT) technique and a genital organ sparing three-dimensional conformal radiotherapy (3DCRT) technique for the treatment of anal canal cancer. Twenty-four patients with anal canal cancer treated between January 2002 and December 2006 were investigated. Each patient was retrospectively planned with the CRT and 3DCRT techniques using the Eclipse planning system (version 7.3, Varian Medical Systems, Palo Alto, CA, USA). Planning target volumes (PVTs) and surrounding organs at risk were contoured. Organs at risk included the bladder, bowel, femoral head and neck, and external genitalia. The two planning approaches were compared using dose volume histograms. Dose volume histograms of the PTV pelvis and PTV inguinal showed comparable PTV coverage between the two techniques. The mean percentage volumes of the PTV pelvis and PTV inguinal receiving at least 95 of the prescribed dose was greater than 99 and 91.5 , respectively. Dose volume histograms of the external genitalia demonstrated that they were well spared by the 3DCRT technique with mean doses of 28.30 and 13.17 Gy for the CRT and 3DCRT techniques, respectively. The percentage volume of bowel and bladder receiving 35 Gy or less was reduced with the 3DCRT technique. The femoral head and neck doses were comparable between the two techniques, with average maximum doses recorded of 40.60 and 50.69 Gy. The results of this study demonstrate that the 3DCRT technique achieves significant sparing of surrounding organs at risk, particularly the external genitalia. This organ at risk sparing was accomplished while achieving comparable PTV coverage with a CRT technique.