Introduction Conjoined twins have multiple congenital anomalies, as well as anatomic fusions; therefore, they also need various surgical procedures and invasive interventions beyond the separation process. We present the anaesthetic management during the colostomy opening in omphalopagus twins and ultrasound-guided (UG) central venous catheterisation (CVC). Case Presentations Case 1 Conjoined twins (both males) were delivered by an emergency caesarean section under general anaesthesia at 34 weeks of gestation. The twins, named as B1 and B2 (Figure 1), had a total weight of 3,620 grams. Ultrasonography revealed single rectum and one set of male genitalia. The transthoracic echocardiogram finding of B1 was normal; however, B2 had patent foramen ovale. On day 6, the twins were taken into the operating room after written informed consent was obtained from parents. The anaesthesia of twins was performed by two teams. They were monitored with electrocardiogram, non-invasive blood pressure and peripheral oxygen saturation. For fluid resuscitation, 5% Dextrose-0.02% NaCl was initiated. Anaesthesia induction for B1 was provided with incremental concentrations of sevoflurane in 100% oxygen (O2). Simultaneously, the ventilation of B2 was provided with 2% sevoflurane. Firstly, B1 was intubated after rocuronium (0.6 mg kg −1) administration, and then the intubation of B2 was attempted; however, he showed excessive movement during intubation. Therefore, rocuronium was also applied to B2, and intubation was successful. A size 2.5 uncuffed endotracheal tube was used, and pressure-controlled ventilation was preferred to adjust the end-tidal carbon dioxide values between 30 and 35 mmHg of both twins. The body temperatures were 35°C and 34.8°C, respectively, at the beginning of surgery. Anaesthesia was continued with 0.2%-1% sevoflurane in 50% nitrous oxide (N 2 O)-O 2 mixture, and additional rocuronium was administered when needed. Cystoscopy and opening of colostomy were conducted. Haemodynamic and respiratory parameters were within normal physiologic limits during anaesthe