A boy in mid-childhood presented with right-sided gynaecomastia, which was excised. He represented and, on review by endocrinology, Tanner staging showed stage 2 left-sided glandular breast tissue and some features of virilisation. His testicular volumes remained prepubertal (3 mL). Testicular ultrasound demonstrated irregular echogenic foci bilaterally, and mucosal freckling was noted. A genetic panel confirmed a de novo STK11 variant, pathogenic for Peutz-Jeghers syndrome (PJS). Aromatase inhibition was chosen in preference to left-sided mastectomy. His growth velocity and bone age stabilised, and left-sided breast budding reduced in size. He continues to have a good cosmetic outcome with preserved height potential 5 years later. In this case, to date, treatment with an aromatase inhibitor has negated the need for further surgery. Pseudopuberty in boys with PJS can lead to a diagnostic and treatment challenge. We present a recent case and review the evolving treatment standards and diagnostic strategies.