A prognostic model was developed by examination of the prospectively recorded presentation characteristics of patients presenting with low grade non-Hodgkin's lymphomas (LGL). A geographically distinct group (Edinburgh and Borders) was excluded in order to test the validity of the model based on the rest of the Scotland and Newcastle Lymphoma Group (SNLG) population. Between 1979 and 1987 506 patients presented with low grade lymphoma according to Working Formulation definition within one of each of the three main pathology categories. The median available follow-up was 47 months. In a multivariate analysis performance status, age, stage, gender and haemoglobin all contributed separately. 25% of all patients had relatively good prognosis with a median survival not reached and 84% alive at 5 years. Conversely for the worst prognostic group of 25% of patients the median survival is 18 months with only 26% surviving at 5 years. Finally for the intermediate group of 50% of all patients, median survival is 69 months with 58% alive at 5 years. These striking prognostic separations are shown also to be valid in sub-group analysis. Thus young patients within any pathology subgroup have been identified with bad prognostic lymphoma for whom novel strategies in therapy should be devised.