Available evidence suggests that both homocysteine and blood pressure variability (BPV) are closely correlated with cardio-cerebrovascular disease. However, no previous study has addressed the correlation between homocysteine levels and 24-h ambulatory BPV. The aim of this study was to investigate the relationship between serum homocysteine levels and 24-h ambulatory BPV in Chinese hypertensive patients. This study consisted of 60 patients, divided into two groups according to the homocysteine level (high-level homocysteine group (n = 15), >= 15 mu M; low-level homocysteine group (n = 45), < 15 mu M). The serum homocysteine, vitamin B12, and folate levels were measured. BPV was determined by 24-h ambulatory blood pressure (BP) monitoring. There were significant differences in 24-h systolic BP-standard deviation (SD), daytime systolic BP-SD, daytime diastolic BP-SD, night-time systolic BP-SD, nighttime diastolic BP-SD, 24-h mean pulse pressure (PP)-SD, as well as serum vitamin B12 and folate levels between the high-level and low-level homocysteine groups. Multivariate linear regression analysis indicated that a high serum homocysteine level was an independent predictor of BPV and that the BPV increased with increasing homocysteine levels. The Spearman's rank correlation test indicated a positive correlation between the serum homocysteine level and the BPV index. In addition, hyperhomocysteinemia was an independent risk factor for BPV, and hypertensive patients with hyperhomocysteinemia had increased BPV. Thus, it is recommended to determine the homocysteine level and BPV index in patients with hypertension.