Mid-cervical kyphosis in diastrophic dysplasia (DD) with cord compression and weakness has been recognized for the last three decades. A strikingly similar situation exists in Larsen's syndrome (LS), an otherwise unrelated problem of weakness with lay joints and dislocations with typical facies. Forty patients with DD were studied of whom seven had cervical spine kyphosis: one patient had spontaneous correction over the ensuing two decades. Seven patients with LS were studied of whom four had cervical spine changes with cord compression. There was one sudden death among the patients with LS and no cases of spontaneous correction. Muscle weakness in DD and LS should lead to evaluation of cervical spine kyphosis with cord compression. Plain films, CT and recently MRI are useful.