Matrix metalloproteinases are believed to play an important role in tumor progression, invasion and metastasis. In order to investigate if the expression of stromelysin-3 (ST3) mRNA could add prognostic information concerning invasive laryngeal cancer and/or be indicative of a high risk for tumor progression in laryngeal dysplasias ST3 expression was analyzed by in situ hybridisation of formalin fixed paraffin embedded laryngeal specimens. Furthermore, all specimens underwent image cytometry (ICM) DNA analysis, and, p53 immunostaining. Invasive epithelial cancer, both localized (T1, T2) cancers, cured, as well as not cured, by radiotherapy, and cases with regional lymph node metastases were studied. Furthermore, high grade and low grade dysplasias, selected for rapid, slow and non-progression, as well as non-neoplastic inflammatory lesions were investigated. Expression of the ST3 gene was found in 9 out of 14 (64%) invasive cancer lesions, and in 3 out of 10 (30%) dysplasias, thus indicating that ST3 expression correlates to tumor progression. The ST3 positive laryngeal cancer lesions displayed a higher degree of DNA aberration than the ST3 negative lesions thus suggesting that ST3 positivity could indicate highly malignant tumors. Of the three ST3 positive dysplasias, the first progressed rapidly to cancer in situ with suspected microinvasion. The second ST3 positive dysplasia progressed to invasive cancer within five months. The third ST3 positive dysplasia had been radically excised and hereby cured. All but one of the dysplastic lesions showed p53 immunoreactivity, and all dysplasias exhibited aneuploid cells. ST3 expression appears to be a late event in the multistage process of carcinogenesis and could prove useful as an indicator of dysplasias with imminent risk for progression to invasive cancer.