Aims: To investigate the occurrence, associations, and impacts of self-reported nocturnal parafunction, daytime parafunction, temporomandibular joint (TMJ) pain, and TMJ clicking in a New Zealand birth cohort of 38-year-old individuals. Methods: A cross-sectional analysis of data from a longstanding prospective observational study of a Dunedin, New Zealand birth cohort was undertaken. A questionnaire was used to measure self-reported nocturnal parafunction, daytime parafunction, TMJ pain, and TMJ clicking, and the short-form Oral Health Impact Profile (OHIP-14) tool was used to measure the impacts of these factors while controlling for personality traits. Results: Of the 912 participants (49.7% female) who were dentally assessed and had completed questionnaire data, 31.6% reported nocturnal parafunction and 48.3% reported daytime parafunction. TMJ pain was reported by 29.4% and TMJ clicking by 34.8%. The prevalence of daytime grinding was significantly greater among women (54.2%) than men (42.5%), as was the prevalence of TMJ pain (34.5% and 24.1%, respectively). Those with parafunction or TMJ symptoms had higher mean OHIP-14 scores, and this difference remained significant after controlling for sex, socioeconomic status, xerostomia, untreated dental caries, missing teeth, and personality traits. Conclusion: People with parafunction or TMJ symptoms have poorer oral health-related quality of life than those without these symptoms. Keywords: adults, epidemiology, orofacial pain, quality of life, temporomandibular dysfunction