Auditory brainstem response (ABR) audiometry is said to be 90% sensitive in the diagnosis of acoustic neuromas. Since gadolinium-DTPA was introduced, magnetic resonance imaging (MRI) is capable of detecting acoustic neuromas as small as 3 mm. Early diagnosis is important, because hearing can frequently be preserved with resection of tumors smaller than 2 cm. At the same time, cost-containment has become a pressing issue in medicine. Auditory brainstem response, although considerably less expensive than MRI, may not be as sensitive as previously thought, particularly for small tumors. Of 753 acoustic neuromas treated at the House Ear Clinic from January 1988 through March 1993, 197 had ABR data available. The 98 males and 99 females ranged in age from 13 to 78 years with a mean of 48 years. The overall sensitivity of ABR was 92.3% using an interaural latency difference for wave V of more than 0.2 ms, and was 81.6% using waveform morphology. There was a statistically significant difference in sensitivity with respect to tumor size. Auditory brainstem response interaural latency difference sensitivity ranged from 100% in tumors larger than 3.0 cm to 83.1% in tumors 1.0 cm or smaller. Waveform morphology was abnormal in 100% of tumors larger than 2.0 cm but in only 76.5% of tumors 1.0 cm or smaller.