Kraepelin's nosology found difficulties on diagnosing some psychotic pictures. Leonhard defined them as cycloid psychosis. Despite its clinical relevance, the diagnosis of cycloid psychosis has been neglected in the psychiatric literature and in the current nosological systems.

To present a case study describing a cycloid psychosis and to examine the clinical validity and nosological status of the concept.

The concept, nosological status, diagnostic features, associated clinical characteristics and the etiopathological variables involved in cycloid psychosis are reviewed.

A case report is presented in detail and a literature review is shortly surveyed.

We report a case of a 44-year-old man with no background until 2005 when he went to work in Holland and developed a sudden onset of behavior disturbance with aggressiveness, sexual disinhibition, coprolalia and persecutory delusions concerning his colleagues. He returned to Portugal and was admitted to our department, sleepy and dysarthric. He was treated with low doses of antipsychotic with quick remission of the symptoms. On 2007 he went to work in Spain and developed a clinical picture of behavior disturbance with psychomotor restlessness and sexual disinhibition. As he was admitted to our department, he showed himself perplexed, almost in mutism. Low doses of antipsychotic overtook the symptoms.

Cycloid psychosis is a valid clinical construct that can be differentiated from the boundary disorders on clinical grounds. It's heterogeneous from the etiopathological point of view, in that many factors seem to be involved to a different degree in most of the patients.