Simultaneous presence of congenital irreducible atlantoaxial dislocation (AAD) and cervical intramedullary astrocytoma has not been previously described and may cause disabling myelopathy. This 55-year-old lady presented with suboccipital pain, spastic quadriparesis, Lhermitte's phenomenon and sphincteric disturbances. Lateral radiographs and magnetic resonance imaging showed irreducible AAD, occipitalized atlas, C2-3 fusion, and,an intramedullary tumor from C2-5 level iso-to-hypointense, non-enhancing, except in a small segment in the dorsal C2 level. A suboccipital craniectomy with C2-5 laminectomy revealed a greyish-white tenacious tumor. The tumor was decompressed using a C2-5 midline myelotomy and duroplasty. An occipitocervical lateral mass fixation was performed. Histopathology revealed a low-grade astrocytoma. At three-month follow-up, her spasticity had decreased and quadriparesis and sphincteric disturbances were persisting. Postoperative lateral radiographs and intrathecal contrast CT scan showed a stable occipitocervical construct. Thus, the suboccipital craniectomy and laminectomy with midline myelotomy and duroplasty facilitated space for progressively expanding intramedullary astrocytoma with irreducible AAD; the lateral mass fixation provided stability at the craniovertebral junction.