Early recognition of the signs and symptoms of mental health disorders is important because early intervention is critical to restoring the mental as well as the physical and the social health of an individual. This study sought to investigate patterns of treatment seeking behavior and associated factors for mental illness.A quantitative, institution-based cross sectional study was conducted among 384 psychiatric patients at Jimma University Specialized Hospital (JUSH) located in Jimma, Ethiopia from March to April 2010. Data was collected using a pretested WHO encounter format by trained psychiatric nurses. Data was analyzed using SPSS V.16.Major depression disorder 186 (48.4%), schizophrenia 55 (14.3%) and other psychotic disorders 47 (12.2%) were the most common diagnoses given to the respondents. The median duration of symptoms of mental illness before contact to modern mental health service was 52.1 weeks. The main sources of information for the help sought by the patients were found to be family 126 (32.8%) and other patients 75 (19.5%). Over a third of the patients 135 (35.2%), came directly to JUSH. Half of the patients sought traditional treatment from either a religious healer 116 (30.2%) or an herbalist 77 (20.1%) before they came to the hospital. The most common explanations given for the cause of the mental illness were spiritual possession 198 (51.6%) and evil eye 61 (15.9%), whereas 73 (19.0%) of the respondents said they did not know the cause of mental illnesses. Nearly all of the respondents 379 (98.7%) believed that mental illness can be cured with modern treatment. Individuals who presented with abdominal pain and headache were more likely to seek care earlier. Being in the age group 31-40 years had significant statistical association with delayed treatment seeking behavior.There is significant delay in modern psychiatric treatment seeking in the majority of the cases. Traditional healers were the first place where help was sought for mental illness in this population. Most of the respondents claimed that mental illnesses were caused by supernatural factors. In contrast to their thoughts about the causes of mental illnesses however, most of the respondents believed that mental illnesses could be cured with biomedical treatment. Interventions targeted at improving public awareness about the causes and treatment of mental illness could reduce the delay in treatment seeking and improve treatment outcomes.