To determine the significance of atypical squamous cells of undetermined significance (ASCUS) in patients 55 years or older. From January 1994, to January 1997, 8,175 cervicovaginal smears were obtained from patients 55 years or older (mean age, 64.8; range, 56-84) at University Hospitals of Cleveland. Ninety-six of these patients were diagnosed with ASCUS only or ASCUS with a qualifying statement on the smear. Patient records, follow-up cervicovaginal smears and biopsies were reviewed for a period of one to four years following the diagnosis of ASCUS. The incidence of ASCUS only or ASCUS with a qualifying statement for patients 55 years or older was 1.8%. The ASCUS:SIL ratio was 2.6:1. An estrogen stimulation test was recommended in two cases. Women older than 55 with ASCUS were three times more likely to be receiving hormonal replacement therapy than similar-aged women with normal cervicovaginal smears. Follow-up cervicovaginal smears or biopsies were obtained on 93 (80 cervicovaginal smears, 13 biopsies). The results were the following: LSIL (13), squamous carcinoma in situ (1) and ASCUS (53); the remainder of the cases were normal. In the patients who received a second diagnosis of ASCUS, follow-up cervi covaginal smears or biopsies revealed low grade dysplasia in six. Although the incidence of ASCUS and the frequency of underlying dysplasia is lower in postmenopausal women than the general population, there is still a real risk that a postmenopausal woman with ASCUS has underlying intraepithelial neoplasia. Therefore, these patients should be managed as is the general population.