Facial expressions convey reliable nonverbal signals about pain and thus are very useful for assessing pain in patients with limited communicative ability, such as patients with dementia. In this review, we present an overview of the available pain observation tools and how they make use of facial expressions. Utility and reliability of facial expressions to measure pain in dementia are discussed, together with the effect of dementia severity on these facial expressions. Next, we present how behavioral alterations may overlap with facial expressions of pain, and may even influence the extent to which pain is facially expressed. The main focus is on disinhibition, apathy and emotional changes. Finally, an overview of theoretical considerations and practical implications is presented for assessing pain using facial expressions in clinical settings.