Double bookkeeping is a term introduced by Eugen Bleuler to describe a fundamental feature of schizophrenia where psychotic reality can exist side by side with shared reality even when these realities seem mutually exclusive. Despite increasing theoretical interest in this phenomenon over the recent years, there are no empirical studies addressing this issue. We have, therefore, conducted a phenomenologically descriptive qualitative study of 25 patients with schizophrenia in which we addressed the following issues: (1) Experience of double reality; (2) Emergence and development of two realities; (3) Truth quality of psychotic or private reality; (4) Insight into illness; (5) Communication of psychotic experiences. The most important result was that most patients felt to be in contact with another dimension of reality. Hallucinatory and delusional experience pertained to this different reality, which patients most frequently kept separated from the shared reality. This other dimension was considered by the patients as being more profound and real. The pre-psychotic and psychotic experiences were difficult to verbalize and typically described as totally different than ordinary experience. Double reality was persistent across remissions. None of the patients considered their condition as an illness analogous to a somatic disorder. Most patients described a vague sense of duality preceding the crystallization of double bookkeeping. This emergence of doubleness was associated with a fundamental alienation from oneself, the world, and others stretching back to childhood or early adolescence. We discuss the results with a special emphasis on the concept of psychosis, clinical interview, treatment, and pathogenetic research.