In order to study the relationship between serum C-reactive protein (CRP) levels, leukocyte count and carotid plaque in patients with ischemic stroke, carotid duplex examination was performed by high-definition imaging (HDI) 5000 triplex system. Serum CRP was measured by nephelometry within 72 h after index ischemic stroke. A lesion was considered a plaque in the presence of a maximum intimal-medial wall thickness (IMT) 1.2 mm. Results of carotid ultrasonography were divided into two groups: M1, normal (IMT < 1.2 mm) and M2, abnormal (IMT > or = 1.2 mm). The results showed that the mean age of M2 was significantly older than that of M1 (69.7 +/- 10.4 versus 62.5 +/- 9.6, P = 0.001). The patients with hypertension and diabetes mellitus (78%, 35% respectively) in M2 were significantly more than those (52%, 18% respectively) in M1 (P < 0.01, P < 0.05). There were 32 (65%) patients with elevated CRP levels in M2, but 33 (46%) patients with elevated CRP levels in M1, with the difference being significant between the two groups (P < 0.05). The levels of serum glucose and leukocyte count (8.1 +/- 5.5, 10.3 +/- 4.0, respectively) in abnormal CRP group were significantly higher than that of normal CRP group (6.4 +/- 2.8, 8.7 +/- 3.4) (P < 0.05, P < 0.05); elevated CRP levels was found in 42 (62%) patients with territory infarction and 23 (43%) patients with lacunar infarction respectively, with the difference being significant between these two groups (P < 0.05). It was concluded that the elevation of CRP levels was an significant clinical index for carotid plaque in patients with acute cerebral infarction.