<p>Hypertension and diabetes mellitus are highly prevalent chronic diseases worldwide, and their coexistence presents a growing public health challenge, particularly in low-resource settings like Ethiopia. Thus, this study aimed to assess hypertension and its associated factors in patients with diabetes mellitus attending a follow-up clinic in central Ethiopia. A health facility-based cross-sectional study was conducted. Study participants were selected using a systematic random sampling method. Data were collected through a structured, interviewer-administered questionnaire and patient record reviews. A binary logistic regression model was employed to examine the association between hypertension and the explanatory variables. Adjusted odds ratios (AORs) with 95% confidence intervals (CIs) were calculated to estimate the strength of associations, and statistical significance was determined at a p-value of &lt; 0.05. A total of 379 patients with diabetes mellitus participated in the study. The prevalence of hypertension was 34.6% (95% CI: 29.8–39.4). Being aged 41–60 years (AOR = 2.26, 95% CI: 1.23–4.15), having type 2 diabetes (AOR = 3.83, 95% CI: 1.07–13.65), the presence of comorbidities (AOR = 2.72, 95% CI: 1.59–4.67), and poor medication adherence (AOR = 2.06, 95% CI: 1.12–3.77) were statistically significant factors associated with hypertension among diabetes mellitus patients. More than one-third of patients with diabetes mellitus had hypertension. Older age, type 2 diabetes, the presence of comorbidities, and poor medication adherence were factors associated with hypertension. Regular blood pressure checks, especially for older patients, managing comorbidities, and improving medication adherence through education and simpler regimens are recommended.</p>