Dr. Maizels is Professor of Urology at Northwestern University's Feinberg School of Medicine and has been an attending pediatric urologist at Children's Memorial Hospital since 1980. He has been helping obstetricians and perinatologists manage fetal urological problems since 1985.

Throughout his career, he has combined his research and clinical talents to advance the treatment of urological birth defects. His research using the chick embryo has revealed mechanisms responsible for the development of renal dysplasia. Dr. Maizels has co-authored original clinical papers on obstetric methods to forecast the outcome of fetuses with fetal hydronephrosis and worked to clarify the meaning of fetal hydronephrosis. More recently, a prospective protocol has shown the benefits of surgery for ureteropelvic junction obstruction vs. the risks of observation alone.

In 1989, Dr. Maizels served as the founding president of the Society for Fetal Urology. This nationally based group has established common methods to grade hydronephrosis by ultrasound and diagnose renal obstruction by well tempered renography.