The purpose of this review is to describe the clinical features, pathology and molecular biology of intraocular lymphomas, which represent a heterogenous group of malignant neoplasms; to propose an anatomical classification of these tumours according to whether they occur in the retina or uvea; and to overview laboratory investigations and highlight factors required for successful biopsy. Recent findings show that retinal lymphomas are high-grade (i.e. aggressive), B-cell malignancies and are associated with a poor prognosis, with most patients dying of central nervous system disease. Immunophenotyping and somatic mutation analyses indicate that these lymphomas are probably derived from early post-germinal centre cells. Primary choroidal lymphomas are typically low-grade (i.e. indolent), B-cell tumours with morphological, immunophenotypical and genotypic features similar to extranodal marginal zone B-cell lymphomas (EMZL) elsewhere in the body. The putative cell of origin is the post-germinal centre (memory) B cell. Primary iridal lymphomas are very rare, with an equal distribution of B- and T-cell types and with a variable clinical course, most patients succumbing to their disease as a result of systemic dissemination. Primary lymphomas limited to the ciliary body are exceptionally rare. Secondary uveal lymphomas/leukaemias occur in patients with advanced systemic lymphoma or leukaemia, respectively. In summary, the term 'primary intraocular lymphoma (PIOL)' is imprecise. It would be preferable to refer to the various forms of intraocular lymphoma according to whether they are retinal, choroidal, ciliary or iridal and whether they are primary or secondary in these locations.