OBJECTIVE Alexithymia is characterized by a difficulty in identifying and describing one's emotions. Recent research has associated differential effects of the alexithymia facets to hypothalamic-pituitary-adrenal (HPA) axis markers during stress. This study aimed to analyze how the facets of alexithymia interact with autonomic reactivity as well as self- and observer-rated anxiety during a social stress task. METHODS With the use of a public-speaking paradigm, skin conductance levels (SCLs) and heart rate (HR) during the defined periods of baseline, preparation, stress, and recovery were assessed in 60 volunteers (42 females, mean age 22.8) categorized as having either high (HDA) or low (LDA) degrees of alexithymia. RESULTS We found smaller SCLs during preparation and speech in the HDA group. Regression analyses indicated that only the alexithymia facet "difficulty in describing feelings" (DDF) was associated with smaller electrodermal responses. In the HDA group, self- and observer-rated anxiety was higher in the HDA than in the LDA group, which was attributable to higher scores in the subscales "difficulty in identifying feelings" (DIF) and "externally oriented thinking" (EOT). CONCLUSIONS Our data support and specify the decoupling hypothesis of alexithymia by showing that the facets of alexithymia are differentially related to autonomic reactivity as well as self- and observer-rated anxiety during social stress.