Microinvasive carcinoma of the uterine cervix (International Federation of Gynecology and Obstetrics Stage IA). In 1985 the International Federation of Gynecology and Obstetrics (FIGO) subdivided Stage IA cervical cancer and specified metric criteria to demarcate Stage IA from Stage IB. Early stromal invasion (Stage IA1) denotes the first invasive protrusions of a carcinoma in situ into the stroma. Microcarcinomas (Stage IA2) are small cancers a number of orders of magnitude larger than Stage IA1 lesions and with a maximum depth of invasion of 5 mm and a maximum horizontal spread of 7 mm; larger lesions are classified as Stage IB. This study reviews 486 patients previously classified as having Stage IA disease. This yielded 344 Stage IA1 and 101 Stage IA2 lesions; 41 cancers were reclassified as Stage IB. Three hundred nine, 89, and 38 patients were followed for greater than or equal to 5 years. One (0.3%) patient with Stage IA1 disease re-presented with Stage IIB disease 12 years after conization. Five (5.6%) patients with Stage IA2 lesions developed invasive recurrences; three died. None of the 38 patients reclassified as having a Stage IB lesion, including 16 who were treated conservatively, developed a recurrence. The FIGO classification is not a guideline for treatment. Stage IA1 lesions can be treated conservatively, but treatment in Stage IA2 must be individualized. Risk factors such as vascular space involvement and confluency are of high sensitivity but low specificity. 