The objective of this study is to examine the expression of matrix metalloproteinase 1 (MMP-1) in invasive well-differentiated thyroid carcinoma (WDTC) and its relation to clinicopathological features. This retrospective case study group included 26 patients with invasive WDTC who were treated at our center between January 1985 and May 2007. Clinical data were collected from the medical files. MMP-1 expression was tested in samples from paraffin-embedded tumor by immunohistochemical staining. MMP-1 expression correlated with laryngotracheal invasion (p = 0.032), multifocality of the tumor (p = 0.044), and presence of regional (p = 0.034) and distant metastases (p = 0.048). In conclusion, the expression of MMP-1 in invasive WDTC is consistent with tumor aggressiveness, manifested by laryngotracheal invasion, multifocality, and regional and distant metastases. MMP-1 expression may serve as a prognostic marker and an indicator for the need for more aggressive surgical treatment.