A hierarchical cluster analysis procedure was used to identify homogeneous subgroups of low back pain patients who show similar pain behavior patterns during a videotaped behavior sample. Subjects, 106 chronic low back pain patients, were divided into 2 samples. The cluster analysis procedure identified 4 very similar subgroups in sample 1 and sample 2. The first subgroup showed a low or moderate level of guarding and a low level of other pain behaviors. The second subgroup showed a high level of guarding and a moderate level of rubbing of the painful area. The third subgroup showed high levels of guarding and moderate levels of bracing and rubbing. The fourth subgroup exhibited a very high level of rubbing and moderate levels of bracing. The subgroups identified may require somewhat different approaches to pain assessment and treatment. The results of this study suggest that the variability in pain behavior evident in low back pain populations may be due to the fact that within these populations there are homogeneous subgroups of patients who differ in the motor pain behaviors they display. © 1990.