Interstitial granulomatous dermatitis (IGD), a rare disease, is well known to be associated with connective tissue disorders, malignancies and several drugs. We describe this first case of IGD in association with chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL). A 66-year-old woman with a 6-year history of untreated CLL/SLL, presented with a 2-month history of progressively worsening eruption of the left thigh, along with fatigue, lymphadenopathy and night sweats. Skin biopsy showed findings consistent with IGD and infiltration of CLL. The eruption was non-responsive to treatment with antibiotics and local steroids. There was a significant improvement in the rash after an initial cycle of chemotherapy (combination therapy with bendamustine and rituximab) and complete resolution by the third cycle, for the treatment of her CLL. We suggest that the possibility of an underlying haematological malignancy should be investigated in patients with a skin rash non-responsive to conventional therapy.