Background. Typologies of anxiety, depression and somatization symptoms were investigated in individuals with no formal mental disorders, making no a priori assumptions about symptom distribution and inter-relationship.

Method. The subjects were 1617 adult primary care attenders from the WHO Collaborative Project on Psychological Problems in General Health Care, with at least three symptoms of anxiety, depression and/or somatization, but with no formal ICD-10 disorders. Analyses were based on the grade of membership model, a multivariate statistical procedure exploring indistinct boundaries between disease categories and preserving the heterogeneity of clinical picture within each category.

Results. Six prototype categories (or pure types) best described the structure of symptoms included in analyses. Pure type I included the full set of somatization symptoms. Pure type II was characterized by most anxiety and depression symptoms. Pure type III resembled generalized anxiety disorder. Pure type IV consisted of individuals reporting sporadic symptoms of anxiety, depression or somatization. Pure type V defined individuals with sleep problems. Finally, pure type VI was characterized by anxiety symptoms, including panic-like symptoms.

Conclusions. These findings provide support to the existence of a mixed anxiety–depression category crossing the diagnostic boundaries of current anxiety and depression disorders. Moreover, criteria of anxiety and somatization disorders may be re-examined to assess whether lower diagnostic thresholds can be identified that both preserve the symptom profile and clinical features of current diagnostic categories and allow for a better characterization of individuals with substantial psychopathology though not meeting the high symptom thresholds required for a diagnosis of formal mental disorders.