A national consensus procedure was organised to define chronic diseases and health conditions in childhood. Based on (1) a systematic literature search on the definitions of chronic conditions in childhood and (2) a theoretical framework of determinants and indicators of health conditions, a definition of chronic conditions in childhood was proposed. This proposal was subsequently modified according to the comments received from 21 Dutch experts (clinicians, researchers and representatives of patient organisations) in two written consultation rounds and one national meeting, until consensus was reached. Consensus was attained on a definition consisting of four criteria: a disease or condition is considered to be a chronic condition in childhood if: (1) it occurs in children aged 0 up to 18 years; (2) the diagnosis is based on medical scientific knowledge and can be established using reproducible and valid methods or instruments according to professional standards; (3) it is not (yet) curable or, for mental health conditions, if it is highly resistant to treatment and (4) it has been present for longer than three months or it will, very probably, last longer than three months, or it has occurred three times or more during the past year and will probably reoccur. This definition was operationalised using the ICD-10 classification of the World Health Organisation (WHO; International Statistical Classification of Diseases and Related Health Problems [ICD], 10th revision, Geneva, Switzerland, 1992). By this systematic and thorough procedure, national consensus on a comprehensive definition of chronic conditions in children which can be used for epidemiological research was reached.