OBJECTIVE: To design and validate a classification system for audit groups working with stillbirth. The classification includes well-defined primary and associated conditions related to fetal death. DESIGN: Descriptive. SETTING: All delivery wards in Stockholm. POPULATION: Stillbirths from 22 completed weeks in Stockholm, Sweden. METHODS: Parallel to audit work, the Stockholm stillbirth group has developed a classification of conditions related to stillbirth. The classification has been validated. MAIN OUTCOME MEASURE: The classification and the results of the validation are presented. RESULT: The classification with 17 groups identifying underlying conditions related to stillbirth (primary diagnoses) and associated factors which may have contributed to the death (associated diagnoses) is described. The conditions are subdivided into definite, probable and possible relation to the death. An evaluation of 382 cases of stillbirth during 2002-2005 resulted in 382 primary diagnoses and 132 associated diagnoses. The most common conditions identified were intrauterine growth restriction/placental insufficiency (23%), infection (19%), malformations/chromosomal abnormalities (12%). The 'unexplained' group together with the 'unknown' group comprised 18%. Validation was done by reclassification of 95 cases from 2005 by six investigators. The overall agreement regarding primary diagnosis was substantial (kappa=0.70). CONCLUSIONS: The Stockholm classification of stillbirth consists of 17 diagnostic groups allowing one primary diagnosis and if needed, associated diagnoses. Diagnoses are subdivided according to definite, probable and possible relation to stillbirth. Validation showed high degree of agreement regarding primary diagnosis. The classification can provide a useful tool for clinicians and audit groups when discussing cause and underlying conditions of fetal death.