By "acute scrotum" is meant a sudden, painful tumefaction in one or both testicles with local and systemic symptomatologies. It can be caused by spermatic cord torsion in about 50% of cases in paediatric age, while in adults such a cause is much rarer. In addition to the clinical examination, Doppler, eco colour-Doppler and scintigraphy with 99mTc pertecnetate may be of use even though these investigations are not often immediately employable. In addition, as the hours pass, the damage caused to the gonad becomes irreversible; this, of course, influences therapeutic conduct. Starting from the description of a recently observed case of torsion of Morgagni's hydatid, the authors discuss the importance of differential diagnosis to protect the vitality of the testicle and show that surgical exploration, in cases where a definite aetiological diagnosis is missing, is the preferable and most rational therapeutic choice.