The purpose of this Grounded Theory based study was to add to the limited understanding about the perception and observation of pain by the formal and informal carers of people with dementia. Thirty-one carers talked about how they know when their person with dementia has pain. Findings showed there is no one set of signs or behaviours that indicate pain in all people with dementia. However, a common pain assessment process amongst carers involved being able to detect deviation from normal behaviours based upon their intimate knowledge of what is normal for their person. A central hypothesis was thus generated from the data that considered that effective pain assessment for people with dementia is dependent on carers having an intimate knowledge of the individual's normal state of being with dementia. Implications for nursing practice are discussed.