OBJECTIVE To reveal the numerical aberration of chromosome 1 and chromosome 17 in cervical neoplasia. METHODS Fluorescence in situ hybridization (FISH) with chromosome-specific repetitive DNA probes was applied on cervical smears of cervical intraepithelial neoplasia (CIN) I, CIN II, and CIN III, and of invasive carcinoma cases, to detect numerical aberrations of chromosome 1 (#1) and chromosome 17 (#17). The cases were histologically classified as CIN I (n = 9), CIN II (n = 12), CIN III [severe dysplasia (n = 14), carcinoma in situ (CIS) (n = 14)], and invasive carcinoma (IC) squamous-cell carcinoma, large-cell nonkeratinizing type (n = 12). FISH was applied on the same cervical smears of these cases after Papanicolaou's staining, and copies in marked atypical cells were counted using a fluorescence microscope. RESULTS The 9.49 +/- 2.59%/9.72 +/- 1.40% (#1/#17) cells showed an aneuploid pattern in CIN I, 22.5 +/- 3.98%/15.5 +/- 3.02% (#1/#17) in CIN II, 44.3 +/- 7.18%/ 45.01 +/- 5.61% (#1/#17) in severe dysplasia, 52.66 +/- 6.32/48.9 +/- 7.55% (#1/#17) in CIS, and 66.22 +/- 3.20%/57.38 +/- 5.35% in IC. The loss of a chromosome in CIN III cases and the gain of a chromosome in CIS and IC cases should be noted (p < 0.01). CONCLUSIONS Because FISH has revealed the numerical aberrations of chromosome 1 and 17 in cervical neoplasia, this is an especially useful method for biological dosimetry and cancer biology.