Background The importance of serum basal tryptase (sBT) levels on patients with venom allergy is highlighted in recent adulthood studies. The aim of this study was to evaluate the sBT levels of venom-allergic children with varying severity of clinical reactions. We also aimed to document the association between sBT levels and severe systemic reactions (SR). Methods Serum basal tryptase levels were estimated by UniCAP (Pharmacia & Upjohn, Uppsala, Sweden). Children who suffered from large local reaction (LLR) or SR after insect stings were included along with healthy control subjects without a history of any local or SR after insect stings. Results A total of 128 children (55 with SR, 18 with LLR, and 55 age and sex-matched control subjects) with a median age of 8.9years (range 3.217.4) were enrolled. Severe SR was encountered in 24 (44%) patients with SRs. The median level of sBT in children with SRs (median, interquartile range) [4.2g/l (3.64.9)] was significantly higher than in children with LLRs [3.1g/l (2.54.0)] and healthy control subjects [2.9g/l (2.33.4)] (P<0.001). Logistic regression analysis revealed sBT4.8g/l as a significant risk factor for severe SR (5.7 [1.521.4]; P=0.01) in children with venom allergy. Conclusions Our results indicate that sBT levels are associated with a higher risk of severe SR in children with insect venom hypersensitivity. Determination of sBT levels may help clinicians to identify patients under risk of severe SRs and optimal and timely use of therapeutic interventions in children with venom allergy.