Background. Hypertension is one of the most common noncommunicable diseases affecting several individuals globally. However, the level of nonadherence to self-care practices, antihypertensive medications, and associated factors among hypertensive patients in a follow-up clinic at Asella Referral and Teaching Hospital is unknown. Objective. To assess the level of nonadherence to self-care practices, antihypertensive medications, and associated factors among hypertensive patients in a follow-up clinic at Asella Referral and Teaching Hospital, Arsi Zone, Oromia Regional State, Ethiopia, in 2020. Methods. An institution-based cross-sectional survey was conducted on 115 hypertensive patients who visited the follow-up clinic at Asella Referral and Teaching Hospital from December 24, 2020, to January 15, 2021. Data were entered into EpiData version 4.2.0.0 and exported to SPSS version 21.0 for statistical analysis. Binary and multivariable logistic regression analysis was used to assess the presence of statistical association between dependent and independent variables. Results. A total of 115 hypertensive patients were enrolled into the study, giving a response rate of 98.29%. The mean age of the study participants was 55.17 years (SD = 17.986). More than half of them (59 (51.3%)) were females. More than half of them (58 (50.4%)) were married. Nearly two-thirds of them (79 (68.7%)) had formal education. The level of nonadherence to self-care practices was 67.0% (n = 77, 95% CI: 60.0, 75.7). Meanwhile, the patient’s level of nonadherence to antihypertensive medications was 16.5% (n = 19, 95% CI: 10.4, 24.3). The multivariable logistic regression analysis showed that age >45 years (AOR = 2.89, 95% CI: 1.16, 7.18), having no formal education (AOR = 1.67, 95% CI: 1.32, 3.74), and having ≤5 years’ duration since diagnoses of hypertension (AOR = 1.56, 95% CI: 1.07, 3.25) were factors significantly associated with nonadherence to self-care practices. Being male (AOR = 2.09, 95% CI: 1.93, 9.59), being married (AOR = 4.22, 95% CI: 1.29, 13.76), and having an average monthly income of ≤2500 ETB (AOR = 1.58, 95% CI: 1.09, 7.08) were factors significantly associated with nonadherence to medications. Conclusion. In the present study, the level of both nonadherence to self-care practices and antihypertensive medications was relatively high. There is a need to initiate programs that could create awareness about adherence to self-care practices and antihypertensive medications among hypertensive patients to improve their level of adherence.