The objective of this study was to verify the reliability of the classifications of perinatal mortality causes. An independent observer coded the cases of perinatal death (n = 152) collected in the Encuesta Confidencial de Mortalidad Perinatal de Barcelona (ECMP, Confidential Perinatal Mortality Inquiry of Barcelona), by using both the Aberdeen classification system (regarding obstetric factors) and the Wigglesworth classification system (according to the initial pathological cause), with the same information used previously by the ECMP Commission. For the Aberdeen classification, the observed concordance index (Po) was 86% and the Kappa coefficient (K) 0.77 (95% CI: 0.68-0.86). For the Wigglesworth classification, the figures were 89% and 0.82 (95% CI: 0.74-0.90), respectively. The disagreement was mainly due to differences in the interpretation of the sequence of death, minimal information available in order to classify the cause of death, and misunderstanding of the existing information. To a lesser extent, the disagreement was caused by a failure to comply with the rules laid down for classifications. The assessment of the causes of death was not significantly influenced by birth weight, gestational age, time of death or the presence of necropsy. These results support the use of classifications of perinatal mortality causes in the context of confidential inquiries.