Adherence to antiretroviral therapy (ART) plays an important role in the treatment outcomes of human immunodeficiency virus (HIV) infection. Poor adherence would result in failure to prevent viral replication as well as an increased risk of developing drug resistance. Adherence to a life long treatment such as antiretroviral therapy is usually a complicated issue that requires careful and continuous collaboration of patient, family and healthcare provider. The objective of this study was to assess adherence to antiretroviral therapy and its associated factors among people living with HIV. This is a health facility-based cross sectional study conducted among adults’ people living with HIV in Omdurman HIV/AIDS centre, Sudan. Data was collected through direct interview using semi-structured questionnaire. There were only 144/846 (17.02%) who adhered to antiretroviral therapy as prescribed by their doctors. The remaining 51.18% were taking the therapy but not regularly, 31.21% were taking it but currently not and 0.59% stated that they have never taken any antiretroviral therapy. Factors associated with poor adherence that have been identified include female gender (Adj. OR = 3.46 (95%CI: 1.46-8.21), P = 0.005), younger age (Adj. OR = 1.14 (95%CI: 1.02-1.28), P = 0.022), being unemployed (Adj. OR = 5.94 (95%CI: 1.51-23.40), P = 0.011), those who were divorced, separated or widowed (Adj. OR = 11.35 (95%CI: 1.74-73.96), P = 0.011) and respondents who perceived that their health status is poor (Adj. OR = 5.21 (95%CI: 1.44-18.81), P = 0.012) or very poor (Adj. OR = 4.04 (95%CI: 1.27-12.81), P = 0.018). Educational level and social support against HIV-related stigma and discrimination were not significantly associated with adherence. Adherence to antiretroviral therapy among the respondents is very poor. Urgent interventions based on modifiable factors and mainly targeting females and younger age group are needed to improve adherence to antiretroviral therapy among people living with HIV.