Objectives: To study factors associated with stability of the diagnosis, and diagnostic shift of acute and transient psychotic disorder (ATPD). Methods: 350 randomized samples from the patients attending outpatient department of LGBRIMH, Tezpur with the diagnosis of ATPD (ICD–10 diagnosis – F23) during the period of last 5 years allowing for a minimum of 3 years follow up, were reviewed. A total of 298 samples were taken for analysis after discarding the rest due to inadequate data. Finally appropriate statistical analysis was done using SPSS version 20. Results: 32.2% of the samples were diagnosed as polymorphic subtype followed by schizophrenia like subtype (26.8%). More than half had stable diagnosis (51 %). 22% were re–diagnosed as schizophrenia and 12.3% as Bipolar disorder. ATPD diagnosis was more stable among those with stress, however it was not significant (p=0.18). Diagnosis of ATPD was significantly more stable among married people (p = 0.038), cases with abrupt onset (p=0.02), and the cases with polymorphic subtype (p=0.04). People with schizophrenic symptoms were significantly (p=0.01) more likely to be re–diagnosed as schizophrenia than those with polymorphic symptoms. Conclusion: Our findings suggest that ATPD is a relatively stable diagnosis. However where diagnostic shift occurs, the majority are re–diagnosed as schizophrenia followed by bipolar disorder