We recently encountered experienced a rare case of transient pupil-sparing oculomotor nerve palsy(PSONP)caused by an aneurysm at the junction of the internal carotid-and posterior communicating arteries(IC/PC AN)in an 87-year-old, non-diabetic woman. She initially presented with diplopia 4 years previously, and was diagnosed, based on incomplete right oculomotor paresis without pupil involvement(PSONP), as external ophthalmoplegia. MR-angiography revealed a long protrusion of the IC/PC AN with posterior-inferior projection, for which she chose to receive conservative management. Thirty nine months later, she presented with another transient PSONP. CT angiography(CTA)showed that the aneurysm was enlarged in the posterior-inferior direction. Two days after this last CTA imaging, the aneurysm ruptured with upward enlargement of the bleb. Despite complete external ophthalmoplegia and ptosis, her pupil involvement was still minimal and transient. By reviewing reported cases and our own case, we found that a narrow and long aneurysm body and posterior-inferior projection are characteristic for the IC/PC AN that causes PSONP, implying a possible mechanism for PSONP by upward compression of the oculomotor nerve. Though rare in its incidence, IC/PC AN could present with PSONP prior to their rupture. Therefore, immediate imaging evaluation in patients presenting with PSONP is essential to prevent devastating rupture events.