Introduction: Globally, it is estimated that 2.2 billion people have a visual impairment, of which around 65.2 million is due to cataract. Cataract is the leading cause of preventable blindness worldwide, with the greatest burden found in low-income countries. That is providing recent epidemiological data is very crucial to design intervention measures. The aim of this study was to assess the magnitude and associated factors of cataract among adults visiting ophthalmic clinic, Debre Markos comprehensive specialized hospital, Northwest Ethiopia, 2020. Methods: The sample size was calculated using single population formula and determined to be 174. All adult participants aged ⩾40 were the source population and those fulfilling the inclusion criteria were the study population. An institutional-based cross-sectional study design using a systematic random sampling technique was conducted from July to August, 2020. Semi-structured questionnaires and patients’ card were used to collect data. Data were entered into epi-data version 4.6 and the analysis was conducted using SPSS-25 software. Data were presented using graphs, tables and texts. Bivariable and multivariable binary logistic regression models were used to identify factors associated with cataract. Adjusted odds ratio with corresponding 95% confidence interval was computed to show the strength of association. A p-value < 0.05 was considered statistically significant. Result: From a total of 174 samples, 158 participated, giving a response rate of 90.8%. The prevalence of cataract was found to be 90 (57%). The variables—age 60–69 years (adjusted odds ratio = 6.667, 95% confidence interval: (1.662, 13.101)); age 70–79 years (adjusted odds ratio = 9.583, 95% confidence interval: (2.840, 32.342)), and single marital status (adjusted odds ratio = 2.945, 95% confidence interval: (1.241, 6.989))—had a significant association with cataract. Conclusion: The prevalence of cataract was found to be very high, which needs immediate intervention. Older age and single marital status were found to be significantly associated with cataract prevalence.