Planning and implementation of oral health education is of more value when oral health-related knowledge, attitudes and practices (KAP) are known. To assess and describe oral health-related KAP of adult patients in the Mangaung Metropolitan Municipality using the theory of planned behaviour. A quantitative descriptive design was used and data were collected from a sample of 207 adult oral health patients using a questionnaire based on the Theory of Planned Behaviour (TPB). Positive responses by participants towards oral-related KAP were regarded as strengthening oral health-related practices. Oral health-related knowledge as reflected by participants' behavioural beliefs (93.7%), normative beliefs (81.1%), subjective norms (70%) and perceived behavioural control (71.9%) strengthened oral health behaviours positively. Participants' control beliefs did not strengthen oral health practices. Participants' attitudes (62.3%), intention (98.5%), actual behavioural control (99%) and behaviour (95.1%) strengthened oral health-related practices. Adult patients generally portrayed behavioural beliefs, normative beliefs, subjective norms and perceived behavioural control that strengthened oral health behaviours positively. Understanding oral health-related KAP of adult patients would assist role players in the health sector to plan evidence based oral health education. Healthcare workers should be sensitive to the KAP of adult patients receiving oral health-related care. Oral health, knowledge, attitudes, practices, theory of planned behaviour. The mouth is an indicator of the state of a person's oral and general health. 1 Oral health is illustrated by the ability to speak, smile, chew, swallow and use different facial expressions without pain and discomfort. This favourable status may therefore be realised when there is an absence of disorders that affect different structures of the mouth, such as those causing possible pain, mouth lesions, tooth decay and gum disorders. 2,3 Worldwide , oral health disorders are reported to affect almost all adults at some point in their lives and these disorders rank among the top 100 conditions known to affect the quality of life. 4 Poor oral hygiene, diet and smoking are some of the risk factors causing oral health disorders in all corners of the world. 5 In Africa, poverty is one of the determinants of oral health disorders, as it predisposes people to a lack of information and poor lifestyle choices. 6 Poor oral health-related information and lifestyle choices can be improved by integrated oral health promotion strategies with the involvement of government,