Objective: To examine the natural history, survival, and prognostic fa
ctors in a sample of Turkish MS patients. Method: This multicenter stu
dy included 1,259 definite MS patients diagnosed according to the crit
eria of Poser et al. Actuarial analysis of selected disability levels
of 3, 6, 8, and 10 achieved with the Expanded Disability Status Scale
(EDSS); a multivariate Cox regression analysis for prognostic factors
related to time to reach EDSS greater than or equal to 6; and Pearson'
s correlation coefficient for individual factors were performed. Resul
ts: The survival (+/- SE) at 15 years from onset was 94.6 +/- 2.9%, an
d at 25 years was 89.0 +/- 5.8%. The disability reached by 15 years wa
s EDSS greater than or equal to 3 in 66.4%, EDSS greater than or equal
to 6 in 41.2%, EDSS greater than or equal to 8 in 10.5%, and EDSS = 1
0 in 5.4%. The most significant unfavorable prognostic factors were pr
ogressive course (relative risk [RR], 3.73; CI, 2.71 to 5.13) and sphi
ncter symptoms at onset (RR, 1.86; CI, 1.23 to 2.82), followed by male
sex, motor symptoms at onset, and a high attack frequency within the
first 5 years. Primary progressive disease was correlated positively w
ith male sex (r = 0.0895, p = 0.001), older age (I = 0.1807, p = 0.000
), and motor (r = 0.1433, p = 0.000) or sphincter symptoms (r = 0.1001
, p = 0.000) at onset, unlike relapsing-remitting and secondary progre
ssive disease. Conclusions: Although a slightly better prognosis is ob
served in the Turkish MS population, early prognostic factors are simi
lar to most of the previous Western series. Primary progressive diseas
e, mostly seen in older men with motor and sphincter involvement at on
set, has a worse prognosis and may represent a distinct behavioral var
iant of MS.