Long-term data on the natural history of traditionally treated cranial base meningiomas are necessary to judge the benefit of modern cranial base techniques for individual patients and to understand when nonradical surgery of a meningioma is in the interest of the patient. The only available means of obtaining such data is investigation of patients treated before the present surgical era. The records of 315 patients who were operated on at Karolinska Hospital between January 1, 1947, and December 31, 1982, were reviewed. Of the patients, 10.8% died perioperatively and 9.7% died within 10 years. The remaining patients were followed for 10 to 36 years (mean, 18 yr). The 5-year recurrence rate was 4% for patients undergoing radical surgery (Grades 1 and 2) and 25 to 45% for patients undergoing Grade 3 or 4 operations. Follow-up periods longer than 5 years revealed that 16% of Grade 1 and 20% of Grade 2 patients had symptomatic recurrences, whereas a majority of Grade 4 and 5 patients showed symptomatic progression. Forty-two of 69 patients who underwent Grade 4 or 5 operations died as a result of their tumors, usually within 10 years after the first operation. No patients who underwent Grade 4 or 5 operations were free from symptomatic progression after 20 years. The tumor progression or recurrence was usually detected within the 1st 10 years, but late recurrences were seen < or = 25 years after the operation. The worst outcome was found in medial sphenoid wing/clinoidal meningiomas and in tumors invading the cavernous sinus. Subfrontal tumors showed unexpectedly high recurrence rates, with a mortality rate < or = 14% in the late phase. The findings emphasized the necessity to plan the management of patients with cranial base meningiomas according to a 10- to 20-year perspective. Patients must be followed to evaluate the treatment results and to detect recurrences. Nonradical surgery must be viewed as a temporizing or palliative measure; a continued search for means of radical tumor treatment is warranted in these often surgically difficult tumors.