We investigated the association between personality disorders (PDs) and attachment patterns, and examined the construct validity of attachment patterns against adaptive functioning. We used a multimeasure multi-informant approach, which allowed us to disentangle the effects of the methods and to examine the utility of the various methods for measuring these constructs. The participants included 80 clinicians and 170 clinical outpatients, recruited via convenience sampling. Results showed that secure attachment was positively associated with adaptive functioning, whereas insecure patterns were negatively associated with adaptive functioning. Both categorical and dimensional PD diagnoses were associated with insecure attachment patterns. However, after controlling for comorbidity among the PD diagnoses, only some findings remained significant, most notably the association between borderline PD and the clinicians' assessment of preoccupied and incoherent/disorganized attachment, and the patients' self-reported attachment anxiety. Our findings underscore the importance of controlling for comorbidity in examining the associations between attachment patterns and PDs.