A Swedish/Norwegian head and neck cancer study was designed to assess prospectively the levels of mental distress and psychiatric morbidity in a heterogeneous sample of newly diagnosed head and neck cancer patients. A total of 357 patients were included. The mean age was 63 years, and 72% were males. The patients were asked to answer the HAD scale (the Hospital Anxiety and Depression scale) six times during 1 year. The number of possible or probable cases of anxiety or depression disorder was calculated according to standardized cut-offs. Approximately one-third of the patients scored as a possible or probable case of a major mood disorder at each measurement point during the study year. There were new cases of anxiety or depression at each time point. The anxiety level was highest at diagnosis, while depression was most common during treatment. Females were more anxious than males at diagnosis, and patients under 65 years of age scored higher than those over 65. Patients with lower performance status and more advanced disease reported higher levels of mental distress and more often scored as a probable or possible cases of psychiatric disorder. Our psychometric analyses supported the two-dimensional structure and stability of the HAD scale. The HAD scale seems to be the method of choice for getting valid information about the probability of mood disorder in head and neck cancer populations. The prevalence of psychiatric morbidity found in this study emphasizes the importance of improved diagnosis and treatment.