Muscular patterning can be a contributor of positional posterior shoulder instability. Failure to recognize this pattern may lead to unnecessary surgical treatment with high failure rate. We analyzed the results of a new simple clinical test (hand squeeze test). The test is regarded positive, if during squeezing with the contralateral hand and elevation of the involved arm, in pronation, no posterior shoulder dislocation occurs. The test is regarded negative if posterior dislocation does occur regardless of the "hand squeeze". The patients with positive test were treated conservatively. Ten patients (12 shoulders) were treated between July 2006 and July 2010. The 'hand squeeze' test was positive in 8 patients (10 shoulders) and negative in 2 patients (2 shoulders). Both patients with a negative sign had structural lesions in the glenohumeral joint confirmed on arthro-MRI and were treated operatively.