A detailed histologic study has been completed on 125 patients with squamous cell carcinoma of the cervix invading to a depth no greater than 5 mm. Depth of invasion was 3 mm or less in 73% and 3.1 to 5 mm in 27%. The median width was 4.8 mm (range 0.08 to 20 mm). Most of the lesions were multifocal (82%); the number of invasive foci correlated well with increasing width and depth of invasion. Lymphvascular space invasion was found in seven patients, none of whom had lymph node metastases, although in one a single focus of carcinoma was present in the parametrium. Therapy consisted of radical hysterectomy and pelvic lymphadenectomy in 55% of the women, including 43 patients with lesions invading less than 3 mm. There was tumor metastatic to lymph nodes in only one of 69 patients with dissected nodes (1.4%). The mean follow-up time was 5.0 years; there was one recurrence (cervical intraepithelial neoplasia only). This study and a survey of the recent literature imply that tumor pattern, width, and confluence can be ignored in lesions invading to 5 mm, and that the most important factor to consider in therapy planning is depth of invasion. The following guidelines are proposed. In lesions without lymphvascular space invasion, those invading the stroma to no more than 3 mm may be treated with a total abdominal or vaginal hysterectomy. In lesions invading between 3 and 5 mm, a total abdominal hysterectomy and a pelvic lymphadenectomy seem adequate therapy.(ABSTRACT TRUNCATED AT 250 WORDS)