Objective: To evaluate the wheal diameter in allergy skin-prick tests (SPT) with cow's milk extract (CM) comparing tolerant and persistent patients. Method: A retrospective cohort study involving database analysis of children with diagnosis of cow's milk protein allergy (CMPA) mediated by immunoglobulin E in a specialized outpatient clinic that regularly performed SPT between January 2000 and July 2015. Patients were allocated into two groups: tolerant or persistent. Comparisons were made at diagnosis and over time between tolerant and persistent patients using Fisher's, Mann-Whitney or Wilcoxon tests and significance level at 5%. Results: After applying inclusion and exclusion criteria, the sample includes 44 patients (29 tolerant and 15 who persisted with CMPA). In the tolerant group, the medians of SPT were: 6 mm at diagnosis and 2 mm at the development of tolerance; a significant difference (p<0.0001) was found. In the persistent group, the median SPT at diagnosis was 7 mm, while in the last SPT it was 5 mm, with no statistical difference (p=0.173). The comparison of medians in the last SPT between groups was significant (p=0.001), with a reduction greater than 50% in SPT in the tolerant group. Conclusion: Serial SPTs were useful for diagnosis, and a decrease higher than 50% in diameter can indicate the moment to perform oral food challenge (OFC) tests, helping to detect tolerance in CMPA.