Recent studies have shown that the efficacy of benzimidazole drugs is influenced by the intensity of trichuriasis. Therefore, the objective of this study was to determine the efficacy of albendazole (ALB) and mebendazole (MBZ) administered randomly for 1 (ALB×1 and MBZ×1) or 2 days (ALB×2 and MBZ×2) to 385 school children with heavy-intensity trichuriasis (mean faecal egg counts (FEC) >1000 eggs per gram of stool (epg)) in Jimma Town, Ethiopia. The efficacies (95% confidence intervals) by means of reduction in faecal egg counts (FECs) were 29·3% (-9·9-56·2), 60·0% (48·5-70·9), 73·5% (64·2-81·3), and 87·1% (81·4-91·2) for ALB×1, MBZ×1, ALB×2, and MBZ×2, respectively. These observations highlight that assessment of the anthelmintic efficacy of existing or new compounds against Trichuris trichiura should be assessed under varying levels of infection intensity.