In much of sub-Saharan Africa, lumbar punctures (LPs) are performed less frequently than indicated. This is often attributed to patient/family refusal; however, other factors have not been systematically evaluated. We investigated predictors of LP performance for a prospective cohort of people with HIV and new-onset seizures at three hospitals in Zambia. We enrolled 257 participants, including 184 (72%) adults and 144 (56%) urban participants. LPs were performed for 65% of adults and 33% of children, and for 69% of urban and 38% of rural participants. In multivariate logistic regression analyses, LP completion was significantly less likely at one rural site and among children compared to adults. The worst WHO HIV disease stage was associated with increased odds of undergoing LP. Low LP completion rates in Zambia are multifactorial and related to health system and provider factors and patient/family preferences. Further research is necessary to understand this complex problem and develop interventions to improve LP uptake.