The prognostic significance of immune cell infiltrates in surgically resected human lung cancer was investigated in 710 patients. Lymphoid infiltrates were quantified on both standard H&E stained sections and, in a subset of 95 cases, using immunohistochemistry and antibodies to CD3, CD8, CD57, CD68, CD79a and S100 to identify various immune cell types. Subjective grading (low, moderate, high) of lymphoid cell infiltrates on H&E sections of tumour and measurement, using image analysis, of overall level of tumour infiltration by any of the immunohistochemically labelled specific immune cell types of the stained sections showed no prognostic significance. However, when a distinction between peritumoural and intratumoural infiltration by particular cell types was made, intratumoural infiltration by high levels of CD3+ and S100+ cells was associated with longer post-operative survival (P = 0.02 and P = 0.045, respectively). In lung cancer, subjective assessment of tumour lymphoid infiltration and overall levels of infiltration by particular immune cell types carries no prognostic significance. Intratumoural infiltration by relatively high numbers of CD3+ T-lymphocytes and Langerhans cells (S100+) is associated with a better patient outcome.