Stellate ganglion block is a procedure frequently used for the management of patients with chronic sympathetically mediated pain affecting the arm, neck or head. We studied the effect of stellate ganglion block on ipsilateral phrenic nerve function, and hence diaphragmatic strength, in 11 adult patients with chronic sympathetically mediated pain. Pre- and post-block forced vital capacity (FVC) measurements were recorded using a pneumotachograph and a Magstim nerve stimulator was used to generate pre- and post-block twitch mouth pressures (P(TWM)). This device can be used to stimulate the phrenic nerves and hence the diaphragm. The resulting change in airway pressure was measured at the mouth and has previously been shown to reflect diaphragm strength. There was no statistically significant difference in FVC or P(TWM) pre- or post stellate ganglion block. In conclusion, a stellate ganglion block has no adverse effect on ipsilateral phrenic nerve function or diaphragm strength in healthy adult patients.