Background: Oral immunotherapy (OIT) seems to be a promising treatment for hazelnut allergy but the available data is limited. Our objective was to evaluate the proportion of patients desensitised after hazelnut OIT, as well as to evaluate the proportion and type of adverse events (AEs) occurring during OIT and to identify clinical and biological factors predictive of OIT success. Methods: Single-center retrospective study, including pediatrics patients. Oral food challenge (OFC) was performed before and after OIT. For each patient, we collected clinical data and the level of hazelnut IgEs f17, nCor a 9, rCor a 14, at the time of the 2 OFCs. Results: After 12 months of OIT, 52.2% of children were desensitized. Those not desensitized increased their reactogenic dose by 6-fold. One-third presented an AE, mostly non-serious. They were significantly more likely to be desensitized if the levels of hazelnut IgE f17, nCor a 9, and rCor a 14 were initially low. Predictive thresholds of 16.3 kUA/L for hazelnut IgE f17 (p=0.0066) and 4.13 kUA/L for rCor a 14 (p=0.0447) were calculated with an NPV of 85%. Conclusion: Hazelnut OIT is effective in inducing tolerance in 52.2% of children. Children with lower specific IgEs (hazelnut f17, nCor a 9 and rCor a 14) were significantly more likely to achieve desensitization after 12 months of OIT. Predictive thresholds for f17 and rCor a 14 were defined above which the risks of failure of OIT are high.