BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative pathology that disrupts processing of facial expressions of emotion. The impairment was demonstrated for negative emotions in tasks of matching, discriminating, and labeling facial expressions but no study has included the expression of pain in its protocol. OBJECTIVE: The objective was to study the processing of emotional facial expressions in AD with a particular interest in pain expression. METHODS: Twenty-seven controls, 15 mild AD patients, and 15 moderate AD patients had to perform four emotional tasks: identification of facial expressions, matching pain expressions, discriminating the intensity of pain expressions, and judging pain intensity. RESULTS: Some emotions were less efficiently recognized by AD patients compared to controls (p < 0.001), specifically fear from the mild stage (p < 0.05), pain and disgust from the moderate stage (p < 0.05 and p < 0.001 respectively). The Exploratory Factor Analysis showed that recognition of pain and recognition of other discreet emotions were underpinned by two different latent factors. Performances on pain expression matching task and pain intensity discrimination task did not differ by group. (p = 0.334 and p = 0.787 respectively). Finally, moderate AD patients judged the pain less intensively than the Control group for both, moderate, and severe pain intensity (p < 0.001). CONCLUSION: Our data suggest that AD disrupts the recognition of pain expression along with recognition of fear and disgust. Additionally, AD patients seem to underestimate pain intensity compared to controls. The self-rated pain scales should be adapted to the pain processing deficit of AD patients.