This paper reports the findings of a study investigating the smoking behaviours of a community-based psychiatric population. Using a qualitative, grounded theory approach, the four diagnostic categories of schizophrenia, bi-polar affective disorder, depression, and personality disorder were studied (24 interviews in total) in order to identify similarities and differences in smoking behaviours and perceptions of links between illness and cigarette smoking. A number of theoretical constructs emerged from the data, many of which confirm and enhance current understandings of issues, such as the role of cigarettes in managing the symptoms of illness. However, several themes not found in the existing literature also emerged. Smoking was found to play a significant existential role in the lives of participants: alleviating the effects of stigma, promoting positive and negative freedoms, and providing core needs as part of quality of life decisions. Perceptions of the nature and degree of interaction between psychiatric symptoms and the 'need' to smoke were also found to be significant. Variations in smoking between the different diagnostic groups were also found, in particular in the process of smoking itself the nature of the nicotine dependence as predominantly physical or psychological, attitudes towards the quitting process and sense of control, and the degree of significance of existential factors. The research findings suggest that we may be able to add new methods to our current ways of intervening to assist people with a mental illness who want to quit smoking. Differences in perceptions and patterns of use suggest that intervention may be more effective if psychiatric diagnosis is also taken into consideration. Because the paper is descriptive and hypothesis generating, its findings need to be tested using a larger sample.