Pediatric lymphoma is common in sub-Saharan Africa, where survival estimates are often based on limited follow-up with incomplete retention, introducing potential for bias. We compared follow-up and overall survival (OS) between passive and active tracing within a prospective cohort of children with lymphoma in Malawi. Median follow-up times were 4.4 months (interquartile range [IQR] 2.0-9.4) and 10.8 months (IQR 6.2-20.6) in passive and active follow-up, respectively. Twelve-month overall survival (OS) was 69% (95% confidence interval [CI] 54-80) in passive and 44% (95% CI 34-54) in active follow-up. Passive follow-up significantly overestimated the OS and underestimated the mortality. Efforts to improve retention in regional studies are needed.