To identify the psychiatric illnesses in patients with hematological/oncological disorders encountered during blood and bone marrow transplantation.Cross-sectional study.Bismillah Taqee Institute of Health Sciences and Blood Diseases Centre, Karachi from December 2002 to December 2005.All consecutive patients, aged 15 years and above, who fulfilled inclusion and exclusion criteria and underwent blood and bone marrow transplantation, were enrolled in this study. Psychiatric assessment comprised of a semi-structured interview based on Present Status Examination (PSE). The psychiatric diagnosis was made on the basis of International Classification of Diseases (ICD-10) system of classification devised by W.H.O.Eighty patients, who fulfilled the inclusion criteria, were inducted in this study. Thirty (37.5%) cases were found to have psychiatric disorders. Out of the total, 60 (75%) were males and 20 (25%) females. Adjustment disorder was the most frequent diagnosis (n=12), followed by major depression (n=7). Rest of the diagnoses made were generalized anxiety disorder, acute psychotic disorder, delirium and depressive psychosis.High psychiatric morbidity associated with blood and bone marrow transplantation was observed. It indicates the importance of psychiatric intervention during the isolation period of BMT as well as pre-transplant psychiatric assessment and counseling regarding procedure.