To determine the incidence of clinically significant lesions in long-term follow-up after a diagnosis of inadequate squamous cellularity using former and new criteria, we reviewed conventional Papanicolaou (Pap) smears (January-December 1998) for adequacy based on the Bethesda System 2001 criterion. Of 23,302 Pap smears evaluated in our laboratory, 114 (0.489%) were classified as unsatisfactory and 245 (1.051%) as "satisfactory but limited by" based on the 10% rule. Follow-up information for 5 years was obtained for 172 patients without a concurrent cervical epithelial abnormality: 25 (14.5%) had squamous abnormalities (atypical squamous cells, 22; low-grade squamous intraepithelial lesion, 2; and high-grade squamous intraepithelial lesion, 1). With the Bethesda System 2001 criterion, 167 (97.1%) of 172 smears had inadequate squamous cellularity and 5 (2.9%) were adequate. No differences in the incidence of squamous abnormalities detected on follow-up were noted between patients with unsatisfactory Pap smears owing to inadequate squamous cellularity and patients with satisfactory and negative smears. Our findings raise the question whether patients with unsatisfactory Pap smears and a negative history of gynecologic diseases require repeated Pap smears within 2 to 4 months as suggested by the American Society for Colposcopy and Cervical Pathology guideline.