Objective: To investigate the Sonic Hedgehog (SHH) signalling molecules and activated leukocyte cell adhesion molecule (ALCAM) expression in the mechanisms regulating invasion and metastasis in oral squamous cell carcinoma (OSCC). Methods: The expressions of SHH signalling molecules Gli family zinc finger 1/2 (Gli1/Gli2), as well as ALCAM expression, was analysed in 101 OSCC patients by immunohistochemistry. The potential relationship between Gli1/Gli2 and ALCAM in regard to invasion and metastasis were studied by western blot, invasion and wound-healing assays. Results: Gli1, Gli2 and ALCAM were expressed in 54.5%, 49.5% and 47.5% of the 101 OSCC specimens, respectively. High expression of ALCAM was associated with shorter survival in the patient population (P = 0.018), which was independent of other clinical parameters. Notably, when both ALCAM expression and positive nodal status were considered, an enhanced prediction of clinical outcomes was achieved (P = 0.001). In OSCC cell lines, down-regulation of ALCAM resulted in reduced cell invasion and metastasis. Importantly, SHH activation increased the half-life of ALCAM leading to ALCAM accumulation and increased cell invasion and migration. Conclusion: ALCAM over-expression in OSCC is an independent prognostic factor for OSCC patients. Its over-expression may be the result of the activation of the SHH signalling pathway and contributes to OSCC progression. Keywords: ALCAM, Gli1, Gli2, invasion, migration, OSCC