In a prospective study, from September 2000 to September 2001, all ureteroscopies ( n=140) were performed under local and intravenous patient controlled analgesia using continuous infusion of remifentanil (Ultiva). The dosage of 0.15 micro g/kg/min was adapted to changing intraoperative pain (range 0.08-0.30 micro g/kg/min). Preoperative sedation with midazolam 2 mg was given 5 min prior to ureteroscopy. The efficacy of monitored anesthesia care ("Big MAC") was quantified by the patient using a visual analogue pain scale. A total of 97.1% (136/140) of the procedures were performed and finished under remifentanil. Only four male patients underwent conversion to general anesthesia due to insufficient analgesia. All but one patient would choose remifentanil again for first line anesthesia. Significant differences in pain scale values were noticed for male/female patients and ureteroscopies above/below the iliac vessel crossing. Side effects were rare being mainly hypoxic events (pO(2)<90% in 5.1%). Indication, intraoperative procedure, average surgery time (24 min), complications and primary success rate (96.6/90/63.3% stone free for distal/mid/proximal ureter, respectively) did not differ from the control group under general anesthesia. Ureteroscopies with remifentanil are safe, universally applicable because of refifentanil's organ independent esterase metabolism and as effective as general anesthesia. There is no need for PACU stay for patients due to the ultra-short drug half-life, and therefore remifentanil is cost effective and perfect in an outpatient setting.