Objective: The aim of the study was to assess the diagnostic delay in pediatric patients with primary immunodeficiencies (PID) at a tertiary care hospital in Peru. Methods: A descriptive study was carried out in which patients from a third-level referral center in Peru were included. Those without a specific diagnosis of PID were excluded. Data was collected by reviewing the medical records and interviewing patients’ family members. Results: A total of 45 patients with a mean of 7.4 years (SD = 4.3) were studied. The most frequent diagnosis was predominant antibody defects (35.5%), and the diagnostic delay had a median of 12.17 months (IQR 5.1–30.3). Conclusions: The most frequently diagnosed group of PID was predominant antibody deficiency. The overall median diagnostic delays for PID and predominant antibody deficiency were 12 and 14 months, respectively. Even though early detection of PIDs is crucial for effective treatment, current available laboratory tests required for PID diagnosis are both complex and expensive. Early detection and management of these pathologies cannot be achieved without training non-specialist health professionals in the diagnosis of PID, as well as integrating multidisciplinary and multi-center cooperation at both national and international levels.