Patients with stage II reflex sympathetic dystrophy syndrome (algodystrophy) often describe a sensation of beneficial warmth in the affected limb when receiving acupuncture treatment. In a case control study of 10 patients with unilateral algodystrophy stage II, and 10 healthy sex and age-matched controls, we investigated whether acupuncture has an effect in blood volume flow and correlated this with a clinical assessment. Blood volume flow was measured by duplex sonography before, during, and after acupuncture. During acupuncture, blood volume flow increased significantly (+31.1%, p (one-tailed) = 0.024) in the patients' effected limbs (by algodystrophy) compared with the patients' untreated limbs (contralateral). It was also elevated compared with the controls' treated limbs (+23.9%, p = 0.046). The corresponding data after acupuncture were +29.5%, p = 0.057 and +38.3%p = 0.014. All but one patient reported improved symptoms. However, only subjective improvement in function, not pain, was positively correlated to the increase in blood volume flow. In patients with algodystrophy stage II, a significant increase of blood volume flow was attributed to acupuncture and was correlated to functional improvement.