This retrospective cohort study of 383 patients with NFPMs reports the following principal findings: (1) Residual disease on the first post-operative scan was a significant risk factor for NFPMs regrowth and associated with a higher risk of re-operation and radiotherapy; and (2) Ki-67 antigen expression in the resected pituitary adenoma was not a significant risk factor for re-operation, albeit higher in young patients and those that went on to receive radiotherapy. The gene discussed is MKI67; the disease is pituitary gland adenoma.