BACKGROUND: Retention of patients in ART care is a major challenge in sub-Saharan programs. Retention is also one of the key indicators to evaluate the success of ART programs. METHODS AND FINDINGS: A retrospective review of 1500 randomly selected medical charts of adult ART patients from a local non-governmental (NGO) supported ART program in the Democratic Republic of Congo (DRC). Retention was defined as any visit to the clinic in the 4 months prior to the abstraction date. Retention over time and across different sites was described. The relationship between patient characteristics and retention rates at 1 year was also examined. 1450 patients were included in the analysis. The overall retention rates were 81.4% (95% CI: 79.3-83.4), 75.2% (95% CI: 72.8-77.3), 65.0% (95% CI: 62.3-67.6) and 57.2% (95% CI: 54.0-60.3) at 6 months, 1 year, 2 years and 3 years respectively. The retention rates between sites varied between 62.1% and 90.6% at 6 months and between 55.5% and 86.2% at 1 year. During multivariable analysis weight below 50 kg (aHR: 1.33, 95%CI: 1.05-1.69), higher WHO stage at initiation (aHR: 1.22, 95%CI 0.85-1.76 for stage 3 and aHR: 2.98, 95%CI: 1.93-4.59 for stage 4), and male sex (aHR: 1.32, 95%CI: 1.05-1.65) remained as significant risk factors for attrition during the first year after ART initiation. Other independent risk factors were year of initiation (aHR: 1.73, 95%CI: 1.26-2.38 for the year 2007 and aHR: 3.06, 95%CI: 2.26-4.14 for the period 2008-2009), and site. CONCLUSIONS: Retention is a major problem in DRC, while coverage of patients on ART is still very low. With the flattening of funding for HIV care and treatment in sub-Saharan Africa, and with decreasing funding worldwide, maximizing retention during the much needed scaling-up will even be more important.