Objective: Numerous studies have shown a relationship between the duration of untreated psychosis (DUP) in schizophrenia and short-term outcome. However, few studies have investigated the relationships between DUP and the medium-term and long-term outcomes. Furthermore, we are unaware of any reports regarding the relationship between DUP and the ultralong-term outcome. This study aimed to investigate the relationship between DUP and ultralong-term outcome at 28 years in patients with schizophrenia. Method: Patients with schizophrenia completed an interview survey 28 years after their initial psychiatric examination during the period 1979-1980. It was possible to conduct the survey using suitable assessment scales in 31 patients in whom DUP was confirmed. These patients were divided into a short DUP group and a long DUP group on the basis of the median DUP, and the outcomes of these two groups were compared. Results: Longer DUP correlated significantly with poorer symptomatic outcome; degree of social adjustment; and, global functioning. Multiple linear regression analysis found no changes in these results even after controlling for various factors, including gender, age at onset, mode of onset, diagnostic subtype, and premorbid adjustment. Conclusion: DUP adversely affected ultralong-term outcome of schizophrenia after 28 years. This finding supports the need to establish a system to enable early detection and appropriate intervention for patients with schizophrenia to reduce the risk of a deleterious outcome after more than 25 years.