Background: Dietary diversity is the consumption of variety of food items over a reference time. It is one of the important indicators to assess the nutrient adequacy and diversity of diet. However, little is known about dietary diversity among adult HIV patients in Bahir Dar. Objective: To assess dietary diversity and associated factors among HIV positive adults attending Antiretroviral Therapy Clinic at Felege Hiwot Comprehensive Referral Hospital, in Northwest Ethiopia. Method: An institution based cross-sectional study conducted in Felege Hiwot Comprehensive Referral Hospital in 2019. Systematic random sampling technique employed to select 352 study subjects. Data collected using an interviewer administered questionnaire & chart review. SPSS version 26 used for analysis. The data were summarized with descriptive measures, simple and multivariable binary logistic regression used to determine associated factors. Results: Two hundred nine (59.4%) adults had consumed a diversified diet. The mean individual dietary diversity score was 3.86 ± 1.18. Self-employment status (AOR: 4.60; 95% CI: 1.72-12.27) compared to unemployed, quintiles of wealth index; [the second (AOR: 4.33; 95% CI:1.72-10.89), middle (AOR: 4.40; 95% CI: 1.71-11.31), fourth (AOR: 6.60; 95% CI: 2.36-18.48) and highest quintile (AOR: 9.45: 95% CI: 3.34-26.77)] in reference to lowest quintile, last CD4 count 200-349cells/mm3 (AOR: 8.08; 95% CI: 2.93-22.23) compared to CD4 count < 200cells/mm3, taking first line ART regimen drugs (AOR: 4.49 ; 95% CI: 2.19-9.21) relative to second line, subjects who were not taking cotrimoxazole prophylaxis (AOR: 6.36; 95% CI: 2.54-15.88), ever had nutritional counseling at health institution (AOR: 2.36; 95% CI: 1.08-5.16), having no food preference (AOR: 2.42; 95% CI: 1.14-5.13), and a food secure household (AOR: 3.51; 95% CI: (1.85-6.67)] were associated factors of dietary diversity among adults on ART. Conclusion: This study dietary diversity status is unsatisfactory among adult attending ART clinic. Health institution and health professionals working at ART clinic shall strengthened their efforts to sustain the nutritional counseling service and ART adherence at health institution and encourage the patients to avoid food preference for their meal. It is vital to ensure household food security of adults on ART.