Systemic lupus erythematosus (SLE) often coexists with other diseases. Diabetes mellitus (DM) is an example and patients with overlap SLE-DM can present with clinical features common to both disorders. In this review, we describe the patients with overlap SLE-DM, focussing on the clinical features common to both diseases that these patients can present, and on the challenges of managing such complications. A detailed review of the patients' notes (n = 485) was performed. At every outpatient appointment the patients' urine was tested for glucose, protein and blood. Patients with persistent glycosuria were investigated with fasting blood glucose and a glucose tolerance test to help make the diagnosis of DM. Particular note was made of those patients whose symptoms could be due to SLE, DM or both. Nine patients with DM were identified. Three had type 1 DM, four had type 2 DM and two were considered to have steroid-induced DM. Among these patients, three had renal involvement (two with WHO class IV lupus nephritis); two had peripheral neuropathy (one had a mixed sensory and motor neuropathy, one had a sensory peripheral neuropathy); two patients had retinopathy and cataracts and one had angina. The combination of SLE and DM is uncommon but the predisposition to renal, peripheral neuropathy and retinal disease means that great care must be taken when deciding which clinical feature is due to which disease, because active SLE requires additional immunosuppression whereas DM requires optimization of the metabolic control. Interestingly, although in theory patients with SLE and DM are in double-jeopardy of developing atherosclerosis, to date, only one of our overlap patients has developed angina.