Introduction Large granular lymphocyte (LGL) leukaemia is considered a mature T-cell or natural killer (NK) cell neoplasm, characterised by a clonal proliferation of LGL.

Aims To analyse the characteristics and to establish (if possible) the prognostic parameters of these patients diagnosed in a single centre: University Hospital of Donostia.

Methods We retrospectively studied data about 308 patients with LGL leukaemia diagnosed in our centre.

Results The frequency of T-LGL leukaemia and chronic lymphoproliferative disorder of NK cells was 89% and 6.8% respectively, and no aggressive NK-LGL leukaemia was seen in our population. The median age at diagnosis was 65.7 years and male-to-female ratio was 1.08. 59% of our patients were asymptomatic at the time of diagnosis. Most patients presented lymphocytosis and 63.6% more than 20% LGLs in the peripheral blood count, but it has to be taken into account that these results may be influenced by the selection bias of our study, as we recognised these patients as ‘alarms of the laboratory analysers’. Neutropenia was the most common cytopenia, and autoimmune disorders were described in 16.5% of the patients. Only 12 patients (3.9%) required treatment, a much lower percentage that the one reported in the literature, and this is consistent with the fact that patients were less symptomatic than in other series, as we expected. The 5-year and 15-year overall survival was 92% and 87%, respectively.

Conclusions Our patients may represent the even more benign end of the spectrum of clonal T LGL and NK proliferations.