The reliability of a surface EMG scanning procedure was investigated for the right and left aspects of 10 muscle sites using a large clinical sample of 102 chronic pain patients. Two neutral postures (sitting/standing) were systematically studied on three occasions approximately one hour apart on the same day. The multivariate analysis of RMS microvolts indicated no significant effects for Age, Gender, Muscle site, Aspect or Period. The range of the Pearson correlations was 0.41 to 0.94 when all muscle sites, aspects, postures, and periods were considered. The median correlation was found to be 0.64. The pattern of reliability was seen to be slightly higher in the upper back while sitting, and slightly higher in the lower back while standing. The results indicate that with adequate attention to skin preparation, EMG sensors held in place by hand with a light pressure produce reliable results.