Ecthyma gangrenosum is a characteristic skin lesion that is caused by Pseudomonas aeruginosa (P. aeruginosa) in the majority of cases. Systemic P. aeruginosa usually complicates debilitating conditions like leukaemia, burns and cystic fibrosis. We report a patient with underlying hypogammaglobulinemia who developed ecthyma gangrenosum secondary to P. aeruginosa septicaemia, which was potentially life-threatening. Recognition of the characteristic skin lesions with prompt initiation of appropriate antibiotics and intravenous immunoglobulins were life-saving. A review of the English literature reports three other cases of ecthyma gangrenosum in patients with underlying hypogammaglobulinemia.