Metastatic prostate cancer has an unpredictable long-term prognosis. At present, there are few specific predictors to indicate the outcome for the individual patient. We have studied immunoreactivity for type-2 carbohydrate structures, known to be involved in various cell adhesion processes, in patients with metastatic prostate cancer. One group of patients (n = 26) did not progress within 3 years after orchiectomy, while another group of patients (n = 33) progressed within 1 year following castration and survived less than 2 years. Among the parameters studied, sialyl LewisX carbohydrate up-regulation was the only variable showing significant association with poor prognosis (P < 0.01). Sialyl LewisX discriminated between these two outcome groups with 71% predictability and 96% specificity. Our results indicate that up-regulation of sialyl LewisX is associated with hormonal-resistant, aggressive disease. This prognostic marker may, therefore, have an important role in selecting proper treatment for patients with metastatic prostate cancer.