BACKGROUND: Neurocysticercosis is a major cause of acquired epilepsy. Larval cysts in the human brain eventually resolve and either disappear or leave a calcification that is associated with seizures. In this study, we assessed the proportion of calcification in parenchymal neurocysticercosis and risk factors associated with calcification. METHODS: Data for 220 patients with parenchymal NCC from 3 trials of antiparasitic treatment were assessed to determine what proportion of the cysts that resolved 6 months after treatment ended up in a residual calcification at 1 year. Also, we evaluated the risk factors associated with calcification. RESULTS: The overall proportion of calcification was 38% (188/497 cysts, from 147 patients). Predictors for calcification at the cyst level were cysts larger than 14 mm (risk ratio [RR], 1.34; 95% confidence interval [CI], 1.02-1.75) and cysts with edema at baseline (RR, 1.39; 95% CI, 1.05-1.85). At the patient level, having had more than 24 months with seizures (RR, 1.25; 95% CI, 1.08-1.46), mild antibody response (RR, 1.14; 95% CI, 1.002-1.27), increased dose albendazole regime (RR, 1.26; 95% CI, 1.14-1.39), lower doses of dexamethasone (RR, 1.36; 95% CI, 1.02-1.81), not receiving early antiparasitic retreatment (RR, 1.45; 95% CI, 1.08-1.93), or complete cure (RR, 1.48; 95% CI, 1.29-1.71) were associated with a increased risk of calcification. CONCLUSIONS: Approximately 38% of parenchymal cysts calcify after antiparasitic treatment. Some factors associated with calcification are modifiable and may be considered to decrease or avoid calcification, potentially decreasing the risk for seizure relapses