OBJECTIVES:To explore differences in mindfulness facets among patients with a diagnosis of either obsessive-compulsive disorder (OCD), major depressive disorder (MDD), or borderline personality disorder (BPD), and healthy controls (HC), and their associations with clinical features. DESIGN AND METHOD: One hundred and fifty-three patients and 50 HC underwent a clinical assessment including measures of mindfulness (Five Facets Mindfulness Questionnaire - FFMQ), psychopathological symptoms (Symptom Check List-90-R), dissociation (Dissociative Experience Scale), alexithymia (Alexithymia Scale 20), and depression (Beck Depression Inventory-II). Analysis of variance (ANOVA) and analysis of covariance (ANCOVA) were performed to assess differences in mindfulness scores and their associations with clinical features. RESULTS: The three diagnostic groups scored lower on all mindfulness facets (apart from FFMQobserving) compared to the HC group. OCD group had a significant higher FFMQ total score (FFMQ-TS) and FFMQacting with awareness compared to the BPD group, and scored higher on FFMQdescribing compared to BPD and MDD groups. The scores in non-judging facet were significantly lower in all the three diagnostic groups compared to the HC group. Interestingly, higher FFMQ-TS was inversely related to all psychological measures, regardless of diagnostic group. CONCLUSIONS: Deficits in mindfulness skills were present in all diagnostic groups. Furthermore, we found disease-specific relationships between some mindfulness facets and specific psychological variables. Clinical implications are discussed. PRACTITIONER POINTS: The study showed deficits in mindfulness scores in all diagnostic groups compared to a healthy control group. Overall, mindfulness construct has a significantly negative association with indexes of global distress, dissociative symptoms, alexithymia, and depression. Mindfulness-based interventions in clinical settings should take into account different patterns of mindfulness skills and their impact on disease-specific maladaptive cognitive strategies or symptomatology.