To determine the laryngeal muscle activation abnormalities that are associated with speech symptoms in adductor spasmodic dysphonia (ADSD), electromyographic measures of extrinsic and intrinsic laryngeal muscles during speech compared 1) muscle activity when ADSD patients had breaks in words with when they produced the same words without breaks; and 2) muscle activity in ADSD patients during speech without voice breaks with normal control producing phonetically similar words. Simultaneous electromyographic recordings were made from the thyroarytenoid (TA), cricothyroid (CT), sternothyroid (ST), thyrohyoid (TH) and the posterior cricoarytenoid (PCA) muscles during speech testing in 11 ADSD patients and 10 control subjects. Speech breaks were identified and mean muscle activity measured starting 100 ms preceding a voice break and for the remainder of the word. Mean muscle activity level was significantly greater on break than non break words in ADSD patients only for the thyroarytenoid muscle (p<.001). No significant differences were found between the ADSD and control subjects during non break words for any of the laryngeal muscles studied. The results demonstrated that 1) only the thyroarytenoid, of the muscles tested, was affected in ADSD, 2) that muscle activation abnormalities were spasmodic, only appearing when symptoms occurred and 3) no imbalances of muscle tone were evident when speech disruptions did not appear.