Fifty-one patients (mean age, 47.3 years) with moderate to severe periodontal disease and 40 patients (mean age, 48.9 years) with symptoms related to bruxism (occlusal parafunctions such as grinding and/or clenching of the teeth) were compared with regard to periodontal conditions and signs and symptoms of mandibular dysfunction. The bruxists reported more symptoms of pain and dysfunction of the masticatory system than the periodontal patients. The clinical dysfunction index was significantly higher among the bruxists, while there was a similarity between the groups in the variation of occlusal conditions, except for occlusal wear, which was more pronounced in the bruxist group. Attrition was in general positively correlated to alveolar bone height. This correlation was stronger (and statistically significant) for the canines than for other teeth. Attrition was negatively correlated to tooth mobility. It is concluded that patients with moderate to severe periodontal disease and patients with bruxism/occlusal parafunctions are distinctly different with regard to signs and symptoms of mandibular dysfunction. The results support the opinions that there is no or only weak correlation between periodontal disease and bruxism, and between bruxism and occlusal status.