A pattern of neural anomaly has emerged in 10 of the 200 patients treated with ionizing external beam radiation and 915 MHz microwave induced hyperthermia for superficial malignancies. Patients report various sensations in parts of the body which not only are far removed from the treated area, but also are not generated through pathways in the treated areas. The most common sensation was a numbness and tingling in the ipsilateral arm when the chest was being treated. In each case, the applicator was at least three aperture widths from the axilla; the angle with the axilla was approximately 90 degrees, and the applicator was angled from 90-180 degrees to the affected arm. In each case, the sensation was only appreciated when the microwave energy was present. There was no correlation of sensation with level of power application. The sensation would saturate at power densities far below those used to achieve therapeutic heating. One patient reported such a severe "burning" sensation in the arm at the lowest measurable power from the generator that further treatment was discontinued. Only one patient had a demonstrable motor deficit. These effects were patient specific and repeated from treatment to treatment in at least two-thirds of the treatment sessions. Sensitive patients were sporadically distributed throughout the patient population.