ABSTRACT
<p><b>INTRODUCTION</b>The aims of this study were two-fold; to investigate the validity and reliability of the Thai version of the Inventory of Interpersonal Problems (IIP) and to compare the characteristics of the interpersonal problems experienced in a non-clinical sample and psychiatric outpatients.</p><p><b>METHODS</b>A total of 689 subjects (452 non-clinical sample and 237 psychiatric outpatients) completed the IIP-32 and IIP-64, Symptom checklist-90 (SCL-90) and 16 Personality Factor (16 PF) Questionnaire, after which a four-week retest was carried out. Cronbach's alpha was used for internal consistency and the intra-class correlation coefficient was used to determine test-retest reliability. Factor analysis of the IIP sub-scales and Pearson's correlation were used for construct and concurrent validity.</p><p><b>RESULTS</b>Both versions of the IIP showed good internal consistency. Factor analysis revealed two factors that corresponded to the circumplex property. The expected correlation between the SCL-90 and 16 PF subscales reflected the level of concurrent validity. There was a significant difference in the cold, socially-inhibited and self-sacrificing subscales between the non-clinical and clinical samples, while major depressive disorder was found to have a significantly higher score in the subscales of the control dimension, i.e. the non-assertive, socially inhibited and self-sacrificing subscales, than the neurotic and non-clinical groups, whereas, the neurotic group differed from the normative sample in terms of the affiliation axis.</p><p><b>CONCLUSION</b>The IIP-64 and IIP-32 demonstrated their reliability and are suitable for use in either clinical or non-clinical setting.</p>