Background: Hypertension is one of the leading causes of death and physical disabilities. The ankle-brachial index (ABI) is one of the useful indicators of blood pressure with the ability to show the risk of peripheral artery disease. This study aims to investigate the relationship between medication adherence and the ABI lavue in patients with hypertension. Methods: In this descriptive cross-sectional study, 250 patients with hypertension referred to medical health centers in Karaj, Iran were enrolled using a convenience sampling method. To collect data, a demographic form and the 8-item morisky medication adherence scale (MMAS-8) were used. Also, the ABI was measured manually using an acoustic Doppler probe. Data were analyzed in SPSS software, v. 25. Findings: The Mean±SD of the right and left ABI were 1.055±0.134 and 1.036±0.113, respectively. The Mean±SD of MMAS-8 score was 5.88±1.74. It was found that 127 patients (50.8%) had low adherence level, 68 (27.2%) had moderate adherence level, and only 55 (22%) had high adherence level. There was a positive significant correlation between patients’ medication adherence and the ABI value. Moreover, a statistically significant difference was observed in the mean scores of the ABI in patients with three different levels of medication adherence. Conclusion: The medication adherence is poor among hypertensive patients in Karaj. It is related to the ABI such that with the decrease of medication adherence, the ABI value decreases. Therefore, adherence to medication regimen in patients with hypertension can be effective in preventing arterial complications.