Adjustment disorder (AD) was introduced into the psychiatric classification systems almost thirty years ago although the concept was recognised for many years before that. Six subtypes are described based on the predominant symptoms but no further diagnostic criteria are offered to assist the clinician. These are common conditions especially in primary care and in consultation liaison psychiatry where the prevalence ranges from 11-18% and 10-35% respectively. Yet they are under-researched, possibly due to the failure of some of the common diagnostic tools to allow for the diagnosis of AD. Among those to incorporate AD, the concordance between the clinical and interview diagnosis is very poor with the diagnosis being made more commonly in clinical practice than the diagnostic tools allow for. AD is found in all cultures and in all age groups.