OBJECTIVE: To provide an anatomic basis of the occipital transtentorial keyhole approach (OTKA), then explore its feasibility and surgical indication. METHODS: Eight cadaveric heads were prepared for this anatomic study. A longitudinal linear 4-cm skin incision that begun at the upper margin of the transverse sinus, 1.5 cm away from the superior sagittal sinus. This was designed for the OTKA. The keyhole craniotomy and conventional craniotomy were performed sequentially for observation and measurement. RESULTS: The interhemispheric corridor and the supratentorial corridor can be used in the OTKA. The surgical field extended superior to the splenium, inferior to the superior medullary velum, ipsilateral to the middle and posterior parts of the medial and inferior temporal lobe, contralateral to the pulvinar, and anterior to the massa intermedia in the third ventricle. The exposure area of the OTKA was 72.05 +/- 6.26 mm(2) and 182.97 +/- 14.65 mm(2) before and after the tentorial incision, respectively. The exposure area of the conventional craniotomy was 187.28 +/- 20.16 mm(2), which had no significant difference to the OTKA. The working angles of the five target points were all smaller for the OTKA than for the conventional approach. The depth of the posterior third ventricle that could be observed was 14.70 +/- 2.54 mm with the OTKA. CONCLUSIONS: Compared with the conventional approach, the OTKA is a more minimally invasive surgical procedure for treatment of the lesions in the pineal region and the middle and posterior parts of the medial and inferior temporal lobe. However, the working angles are relatively narrow.