OBJECTIVE To assess the safety and efficacy of pelvic floor muscle electrostimulation (ES) in women with stress urinary incontinence (SUI) or mixed UI (MUI, urge and interstitial cystitis), using a new portable electrostimulator (Miniaturo, Biocontrol Medical Inc., Yehud, Israel) which delivers different forms of stimulation for treating these two conditions. METHODS For SUI the stimulator is activated on demand only by a sudden increase in intra-abdominal pressure; for frequency and urgency a milder, continuous ES is used. The intensity of ES can be adjusted according to the patient's sensation. Women were enrolled into the study after satisfying inclusion criteria and pad testing; 23 participated in two study groups, i.e. 16 with SUI and seven with MUI (severe frequency, urgency and urge, and mild SUI). The pelvic floor muscles were stimulated through an electrode inserted paraurethrally, positioned similarly in all patients. In patients with SUI and MUI a pressure sensor was also inserted into the rectum, to record intra-abdominal pressure. Stimulation was applied for 1-4 h in patients with SUI and for 6 h in those with MUI. The evaluation was based on urinary symptoms (frequency, urgency, leaking episodes), quality-of-life questionnaires and pad tests at baseline and during stimulation. RESULTS All patients in both groups improved significantly; of the 16 patients with SUI, nine were completely dry during ES, and the remaining seven had a reduced mean pad weight, from 23 to 6 g (74%). There was no significant reduction in pad weight after sham ES (17 g before vs 24.2 g after). In four patients with SUI who continued ES for 4 h the mean cumulative stimulation time (calculated from the stimulator memory) was 3 min (1.3% of 4 h). In the MUI group there were no leakage episodes during ES and significant reductions in voiding variables (Student's t-test) in all. The mean (Sd) voiding frequency, urinary urgency and leaking episodes decreased from 8.1 (4.2) to 1.9 (1.5), 6.4 (2.3) to 0.7 (1.3) and 2.1 (0.7) to 0.7 (0.5) (all P < 0.001), respectively. CONCLUSIONS The concept of this ES system for treating UI is promising; this study supports the efficacy of this form of ES but no conclusions about clinical efficacy are possible at this stage, and thus a trial to evaluate the safety and efficacy of this implantable device is ongoing.