Introduction. Milligan-Morgan haemorrhoidectomy performed with LigaSure system (LS) seems to be mainly effective where a large tissue demolition is required. This randomized study is designed to compare LigaSure haemorrohidectomy with conventional diathermy (CD) for treatment of IV-degree haemorrhoids. Methods. 52 patients with IV-degree haemorrhoids were randomized to two groups (conventional diathermy versus LigaSure haemorrhoidectomy). They were evaluated on the basis of the following main outcomes: mean operative time, postoperative pain, day of discharge, early and late complications. The time of recovery of work was also assessed. All patients had a minimum follow-up of twelve months (range 12-24). All data were statistically evaluated. Results. 27 patients were treated by conventional diathermy, 25 by LigaSure. The mean operative time was significantly shorter in LS, such as postoperative pain, mainly lower on the third and fourth postoperative day: moreover pain disappeared earlier in LS than CD. The time off-work was shorter in LS, while there was no difference in hospital stay and overall complications rate. Conclusions. LigaSure is an effective instrument when a large tissue demolition is required. This study supports its use as treatment of choice for IV degree haemorrhoids, even if the procedure is more expansive than conventional operation