Objectives: To investigate, in a sample of probable sleep bruxers with and without temporomandibular disorder (TMD) pain, the presence and relationships between clinical jaw-muscle symptoms, and test their associations with jaw-muscle electromyographic (EMG) activity during sleep. Methods: Pain, unpleasantness, tiredness, tension, soreness, and stiffness were scored on a 0–10 numerical rating scale (NRS) in 50 probable sleep bruxers. The sample was subdivided into two groups, i.e., with and without TMD pain. Multiple-night, single-channel EMG recordings were performed. Descriptive data, correlations between the six symptoms, and correlations between symptoms and EMG measures, i.e. EMG events/recording, EMG events/hour, and night-to-night variability in EMG events, were calculated. Results: In the total sample, 90% of the participants reported at least one symptom. Tiredness and tension were the most prevalent symptoms (both 78%), and pain the least (30%). In the TMD pain group, pain remained the least reported symptom (57%). Intensity of symptoms was low to moderate, with tension presenting the highest median in the total sample (NRS 4), the TMD pain group (NRS 5), and non-TMD group (NRS 3). Significant correlations between all symptoms were found in the total sample, but not in the two subgroups. No significant associations between EMG measures and muscle symptoms emerged. Conclusion: Jaw-muscle symptoms other than pain were highly prevalent in a sample of probable sleep bruxers. There were no associations between these symptoms and EMG measures of jaw-muscle activity during sleep. These findings challenge the concept of simple relationships between jaw-muscle activity during sleep and clinical muscle symptoms.