An orthopaedic surgical instrument includes a customized patient-specific surgical instrument having a body. A cutting guide slot extends through the body. A pair of first arms extends posteriorly from the body. Each arm includes a first customized patient-specific negative contour configured to receive a portion of a first corresponding positive contour of one of a patient's femoral condyles. A second arm extends proximally from the body. The second arm has a second customized patient-specific negative contour configured to receive a portion of a second corresponding positive contour of an anterior surface of the patient's femur. A method of performing a surgical procedure is also disclosed.