BACKGROUND: Patients' non-adherence to diabetes medication is associated with poor glycemic control and suboptimal benefits from their prescribed medication, which can lead to worsening of medical condition, development of comorbidities, reduced quality of life, elevated health care costs, and increased mortality. OBJECTIVE: This study aimed to assess medication adherence among patients with diabetes and associated factors in Bisha primary health care centers (PHCCs) in Saudi Arabia. PATIENTS AND METHODS: A cross-sectional study was conducted with a sample of 375 type 1 and 2 Saudi diabetic patients attending PHCCs under the Health Affairs of the Bisha governorate. The participants were aged 18 years and above, and had been taking diabetes medications for at least 3 months. Pregnant women, patients with mental illnesses, and those who were not willing to participate were excluded. Adherence to diabetes medications was measured using the four-item Morisky Green Levine Medication Adherence Scale (MGLS). All participants completed a self-report questionnaire including sociodemographic and clinical variables. Univariate and multivariate analyses were carried out using SPSS version 22. RESULTS: Of all the respondents, 134 (35.7%), 161 (42.9%), and 80 (21.4%), patients had high (MGLS score 0), intermediate (MGLS score 1 or 2), and low adherence (MGLS score ≥3), respectively. Factors associated with the level of adherence in univariate analysis were occupational status (P=0.037), current medication (P<0.001), glycated hemoglobin (A1c) (P<0.001), and number of associated comorbidities (P<0.001). In multivariable analyses, A1c <7 (P<0.001) and no associated comorbidities (P<0.003) variables remained significantly associated with adherence. CONCLUSION: The level of adherence to medication in diabetes mellitus patients in the Bisha PHCCs was found to be suboptimal. The findings point toward the need for better management of primary health care providers' approaches to individual patients, by taking into account their medication adherence levels. Better identification of patients' level of adherence remains essential for successful diabetes treatment.