Jared O Mecha,1 Elizabeth N Kubo,1 Lucy W Nganga,2 Peter N Muiruri,3 Lilian N Njagi,1 Syokau Ilovi,1 Richard Ngethe,2 Immaculate Mutisya,4 Evelyn W Ngugi,4 Elizabeth Maleche-Obimbo1 1Department of Clinical Medicine & Therapeutics, University of Nairobi School of Medicine, Nairobi, Kenya, 2The Palladium Group, Nairobi, Kenya, 3Kenyatta National Hospital, Nairobi, Kenya, 4Division of Global HIV and TB (DGHT), US Centers for Disease Control and Prevention (CDC), Nairobi, Kenya Background: Understanding trends in patient profiles and identifying predictors for adverse outcomes are key to improving the effectiveness of HIV care and treatment programs. Previous work in Kenya has documented findings from a rural setting. This paper describes trends in demographic and clinical characteristics of antiretroviral therapy (ART) treatment cohorts at a large urban, referral HIV clinic and explores treatment outcomes and factors associated with attrition during 12 years of follow-up. Methods: This was a retrospective cohort analysis of HIV-infected adults who started ART between January 1, 2004, and September 30, 2015. ART-experienced patients and those with missing data were excluded. The Cochran–Armitage test was used to determine trends in baseline characteristics over time. Cox proportional hazards models were used to determine the effect of baseline characteristics on attrition. Results: ART uptake among older adolescents (15–19 years), youth, and young adults increased over time (p=0.0001). Independent predictors for attrition included (adjusted hazard ratio [95% CI]) male sex: 1.30 (1.16–1.45), p=0.0001; age: 15–19 years: 1.83 (1.26–2.66), p=0.0014; 20–24 years: 1.93 (1.52–2.44), p=0.0001; and 25–29 years: 1.31 (1.11–1.54), p=0.0012; marital status – single: 1.27 (1.11–1.44), p=0.0005; and divorced/separated: 1.56 (1.30–1.87), p=0.0001; urban residence: 1.40 (1.20–1.64), p=0.0001; entry into HIV care following hospitalization: 1.31 (1.10–1.57), p=0.0026, or transfer from another facility: 1.60 (1.26–2.04), p=0.0001; initiation of ART more than 12 months after the date of HIV diagnosis: 1.36 (1.19–1.55), p=0.0001, and history of a current or past opportunistic infection (OI): 1.15 (1.02–1.30), p=0.0284. Conclusion: Although ART uptake among adolescents and young people increased over time, this group was at increased risk for attrition. Single marital status, urban residence, history of hospitalization or OI, and delayed initiation of ART also predicted attrition. This calls for focused evidence-informed strategies to address attrition and improve outcomes. Keywords: antiretroviral therapy, attrition, lost to follow-up, risk factors, electronic medical records, adolescents, urban