Introduction: Hypertension is a major public health problem worldwide. The disease affects one billion individual and the number is expected to increase to 1.56 million by the year 2025. In Sultanate of Oman, the crude prevalence of hypertension rose by 7% in less than 10 years from 33% in the year 2000 to 40% in the year 2008. Furthermore, 60% of patients with essential hypertension and 70% of diabetic hypertensive patients treated in primary health care facilities have uncontrolled blood pressure. Though uncontrolled blood pressure is of major concern to primary care physicians in Oman, its reasons have not been systematically investigated.. Aim: The overall aim was to reveal the rates and determinants of treatment compliance among patients with essential hypertension attending primary healthcare centers in Muscat govemorate. It also aimed at demonstrating patient's knowledge and perceptions of the diseases as well as the perceived barriers for compliance to pharmacological treatment and life style modifications. Method: The study included 376 patients selected from seven healthcare centers in the six wilayats of Muscat governorate. The cross section study was used to describe patterns and impediments of compliance with pharmacological and non-pharmacological treatment. The case control approach analysis was used to identify the determinants of pharmacological compliance. Pharmacological compliance was determined by self-report of pill count and expressed as percentage of the dispensed pills. Data were collected using a pre-designed questionnaire and the review of health records. The univariate and multivariate logistic regression analyses were used to identify the determinants of treatment compliance and results were judged at 5% level. Results: In this study 78.19% of the patients were fully compliant and 91.22% were pliant with at least 90% of the dispensed pills. Main stated barriers for compliance were forgetfulness, (51.22%), feeling normal blood pressure (13.41%) and fear of getting used to medications (13.41%). Variable proportions of patients were non-compliant with exercising (45.21%), weight regulation (37.50%), restriction of dietary fat (14.10%) and salt (8.24%). Moreover, 41.26% of the smokers were maintaining their habit. Only 28.99% of the patients had a controlled blood pressure in the two visits. Full pharmacological compliance was independently predicted by older age, regularity of follow up, worries about missing pills and knowledge of hypertension. At least 90% compliance was additionally predicted by timing with other medications. The constructed models predicted correctly 97.3% of full compliers and 99.1% of those who are compliant with at least 90% of the dispensed pills. Conclusion: This study revealed a high rate of pharmacological compliance. It also revealed that low proportion of patients has a controlled blood pressure and that compliance to pharmacological treatment did not predict blood pressure control. Further studies are required to investigate the adequacy of the prescribed treatment in achieving the targeted blood pressure levels.