Ossification of the ligamentum flavum in the thoracolumbar spine is rare in young adults. We report two cases in 22 year old males who required surgical treatment. The first patient was obese and hyperinsulinaemic. He had a compression myelopathy below T11 due to extensive posterior ossification. The second patient had an osteoid osteoma of the right pedicle of T11 with ossification of the adjacent ligamenta flava. Both patients benefited from surgical decompression of the spine.