BACKGROUND:Spasticity is one of the most important causes of disability after stroke. In spite of high incidence of spasticity, little is known about the relationship between the occurrence and the development of spasticity. This study aimed to determine risk-factors of post stroke spasticity. METHODS:This was an observational study of 149 persons with first ever stroke. The following parameters were assessed: Stroke severity, Spasticity, Disability and Joint contracture. RESULTS:Prevalence of spasticity was between 17-25% during the first 3 months after stroke. The onset of spasticity was 13.79% and 4.16% at 1 and 3 months after stroke respectively. The prevalence of spasticity in the upper extremity was significantly more than lower extremity at 1 month. Spasticity was significantly more severe in the upper extremity than lower extremity. In patients with hemorrhagic stroke Odds ratios of spasticity was 2.5 times more than persons with ischemic stroke (P = 0.0210. The Odds ratios of severe spasticity at 1 and 3 months were 1.66 and 1.75 times more than the first week (P = 0.024, P = 0.042 respectively). CONCLUSIONS:Post stroke spasticity is more common in persons with hemorrhagic stroke, severe paresis and lower functional abilities. The most incidence of spasticity happens in the first month after stroke.