The aim of this study was to investigate clinical and urodynamic effects of anal MES in children with unstable bladder and micturition problems (nocturnal enuresis and/or daytime incontinence). Seventy-three girls, aged 5 to 17 years, mean age 9.7 years, with cystometrically proved idiopathic detrusor instability and nocturnal enuresis and/or daytime incontinence, were treated by maximal electrical stimulation (MES) for 1 to 2 months. Twenty-one girls, aged 6 to 14 years, mean age 9.3 years, with unstable bladder and micturition problems used only the anal plug without a battery for 1 month and served as the control group. Four and a half months (1-36 months) after the end of treatment, 75% of the stimulated patients were cured or improved by 50% or more. In the control group, 86% of the girls remained unchanged (P < 0.01). One month after the completion of anal MES the average number of monthly nocturnal enuretic episodes fell from 14 to 6.5 (P < 0.001) and the number of daytime incontinence episodes diminished from 3 to 0 (P < 0.001). On an average of 14.5 months after the end of anal MES, enuresis recurred in 20% of cases. Post-MES cystometry showed intensified first desire to void (P < 0.05), as well as an increase in maximum cystometric capacity (P < 0.0001), bladder compliance (P < 0.0001), and volume of the first detrusor contraction (P < 0.01). A statistically significant decline in the number of uninhibited contractions was also noticed (P < 0.001). In the control group, the anal plug did not produce any significant cystometrical changes. Anal MES can be recommended as an effective method for treating nocturnal enuresis and/or daytime incontinence and unstable bladder in children.