Introduction: The androgen insensitivity syndrome is due to an androgen receptor gene mutation and is a condition with variable clinical manifestations. It is an X-chromosome linked recessive inheritance pattern. Objective: To describe the clinical case of a two-year old girl with 46,XY disorder of sex development. Methodology: Medical record and paraclinical tests review at a pediatric hospital. Results: A sex development disorder was diagnosed as complete androgen insensitivity syndrome – Grade 7 – in a girl with a normal external female phenotype with Wolffian duct remnants, presenting a 46,XY chromosome complement due to an intronic mutation affecting the androgen receptor ligand-binding domain. Discussion and conclusion: in prepubertal girls with normal external female phenotype in whom a unilateral or bilateral inguinal mass is identified, the presence of a gonad and a probable case of androgen insensitivity syndrome should be suspected. The conventional karyotype and specific molecular testing enable a diagnosis of sex development disorders and the identification of family or sporadic cases to provide adequate genetic counselling.