ABSTRACT Background Sesame seed allergy is growing with reported fatalities. The diagnosis can be difficult with skin prick test (SPT) and specific IgE (sIgE) often showing discrepant results, and oral food challenges (OFC) have long waiting times and potentially severe reactions. We aimed to assess the accuracy of the basophil activation test (BAT) to diagnose sesame seed allergy. Methods Children aged 6 months to 15 years, needing an OFC to sesame were included. All had OFC to sesame alongside SPT, sIgE to sesame and to Ses i 1, and BAT to sesame. Diagnostic performance was determined by ROC curve analyses, in comparison with OFC outcomes. Results Thirty children reacted to (32% sesame allergic, SA) and 65 tolerated (68% sesame sensitised tolerant, SST) sesame during OFC and 5 (5%) had an indeterminate OFC. SPT to sesame extract or tahini, Ses i 1‐sIgE and BAT to sesame (but not sesame‐sIgE) distinguished SA and SST. The area under the ROC curve for all ages/under 2 years was 0.852/0.901 for BAT, 0.820/0.877 for Ses i 1‐sIgE, 0.823/0.864 for SPT to tahini and 0.614/0.716 for sesame‐sIgE. BAT was the only test whose negative result accurately identified all tolerant children. Using 100% sensitivity and 100% specificity cut‐offs, BAT required the lowest number of OFC. Using SPT and Ses i 1‐IgE to reduce BAT did not change the number of OFC. Conclusions BAT was the only test whose negative results allowed to safely advise on home introduction and required the lowest number of OFC to reach 100% diagnostic accuracy.