Cancer is caused by a series of genomic changes leading directly or indirectly to disturbance of growth, differentiation and tissue integrity. Genomic, transcriptional or posttranscriptional alterations of E-cadherin/catenin complexes that are implicated in various steps of cancer development comprise mutational inactivation, transcriptional downregulation of E-cadherin sometimes accompanied by upregulation of N-cadherin, proteolysis of E-cadherin and posttranslational stabilisation of beta-catenin and plakoglobin. The E-cadherin/catenin complex serves not only cell-cell adhesion but also transduces signals to the nucleus and to the cytoskeleton, either directly or through its connections with multiple other complexes. We review here the expression of E-cadherin/catenin in human cancers, emphasising methods of observation and prognostic interpretation of results. This is illustrated in thyroid lesions from the benign follicular adenoma to the extremely malignant anaplastic carcinoma. The eye is an organ largely neglected by students of cadherins and catenins. The implication of a variety of members of these molecular families in the embryonic development of the eye strongly suggests that disturbances of cadherin/catenin complexes are crucial also in the development of ocular tumours.