A 58-year-old Chinese woman with well controlled type 1 diabetes mellitus presented with acute and progressive bilateral lower limb weakness. Investigations revealed severe hypokalaemia (1.3 mmol/L) and hypophosphataemia (<0.32 mmol/L) with rhabdomyolysis and electrocardiogram changes, without other concurrent biochemical abnormalities. Immediate intravenous and oral potassium and phosphate replacement was initiated with objective improvement in weakness with replenished electrolyte levels. Urine studies confirmed renal potassium wasting. Further history revealed frequent dental caries, xerostomia and recent weight loss. A computerised tomography scan showed atrophy of her salivary glands and a skin lesion biopsied by her GP in the past had been histologically characterised as anetoderma. The constellation of these findings and subsequent positive anti-SSA/SSB levels confirmed her diagnosis of primary Sjögren’s syndrome (PSS). PSS has a wide spectrum of renal involvement and should be a differential diagnosis when investigating interstitial nephritis and electrolyte abnormalities, particularly in patients with coexisting autoimmune conditions.