An eight-year-old boy with bronchial asthma receiving pranlukast suffered from an eosinophilic inguinal tumor and eosinophilia, which completely disappeared three months following the cessation of pranlukast therapy. Leukotriene antagonists (LTAs) are a new group of anti-inflammatory drugs used for the treatment of bronchial asthma [3]. Recently, Churg-Strauss syndrome (CSS) associated with LTAs including pranlukast [2] has been reported, although the precise pathogenic mechanisms underlying the development of this condition remain unclear [1, 3, 6]. CSS is characterized by asthma, eosinophilia and evidence of vasculitis affecting a number of organs [5]. The main histological features include extravascular granulomata, tissue infiltration with eosinophils and necrotizing vasculitis [5]. In this report we describe the occurrence of an inguinal eosinophilic tumor in a patient with bronchial asthma receiving pranlukast. Although the diagnostic criteria of CSS were not fulfilled, this does represent a novel adverse effect of LTAs. An eight-year-old boy with Treacher-Collins syndrome was referred to our hospital for investigation of the left inguinal tumor. The patient had suffered from severe bronchial asthma since 2 years of age and had received treatment with oral theophylline and inhaled fluticasone, cromoglycic acid and procaterol. Oral pranlukast (140 mg/day, 7 mg/kg/day) was started two years before the onset of the present illness. The patient has never taken oral or intravenous corticosteroids previously and the dosage of inhaled fluticasone did not change after the start of oral pranlukast. The patient became aware of the left inguinal tumor and associated discomfort one week before admission but did not complain of any other symptoms including those suggestive of systemic vasculitis. On admission, physical examination revealed a hard, tender and red subcutaneous hard mass (2.0×3.0 cm) in the left inguinal region with associated edema and redness in the left scrotum. The patient was afebrile with a body temperature of 36.4°C. Laboratory studies revealed an eosinophilia (23%, 1748/μl) and an elevated IgE level (1990 IU/l, normal<173). Liver enzymes, renal function, serum electrolytes, C-reactive protein, immunoglobulin and C3 and C4 complement levels were normal. Antinuclear antibody, rheumatoid factor and antineutrophil cytoplasmic antibody were negative whilst the druginduced lymphocyte stimulation test for pranlukast using H-thymidine up-take technique was negative. Computed tomography of the chest and sinuses was unremarkable. Surgical exploration of the left inguinal mass demonstrated that the tumor originated from the left spermatic cord (Fig. 1a). A biopsy of the tumor was performed because the tumor could not be separated completely from the Eur J Pediatr (2007) 166:183–184 DOI 10.1007/s00431-006-0226-9