He has been picketed, bombed and shot by anti-abortion activists, but George Tiller has been swiftly acquitted of charges that he performed 19 illegal abortions in 2003.
"This whole trial was a political trial," Tiller's attorney Dan Monnat said outside the courtroom. Assistant Attorney General Barry Disney denied the charge.
A jury of three men and three women reached a verdict after just 45 minutes.
Disney said: "We respect the jury's verdict," which came after five days of testimony and arguments.
Several dozen protesters attended the trial, demonstrating outside the Sedgwick County courthouse or filling most of the seats in the small courtroom under the watch of two dozen law officers.
Reverend Patrick Mahoney of the Washington-based Christian Defense Coalition, who traveled to Kansas to lead the protests, said the verdict was disappointing but would not have much impact on future challenges to abortion.
"This was an important case, but putting it in perspective, it was not about abortion," Mahoney said.
Tiller, 67, testified that he owns one of only three clinics in the United States that perform late-term abortions, which are performed on fetuses that would be viable outside the mother's womb.
Late-term abortions are legal in Kansas if two independent physicians agree that the mother could suffer irreparable harm by giving birth.
Tiller was charged with having an illegal financial and legal relationship with Kristin Neuhaus, a physician who gave him second opinions required for the procedure. She has not been charged in the case.
Neuhaus and Tiller denied there was anything improper about their financial arrangement. They said Tiller referred patients to Neuhaus, who was paid 250 to 300 dollars by the patients for her opinions.
Tiller said aspects of their relationship -- such as allowing Neuhaus to use his clinic to examine patients -- were necessary because of the harassment patients are subjected to when visiting his clinic.
His practice, which had patients from around the world, has been targeted by abortion protesters for decades. His clinic has been bombed and an anti-abortion activist shot him in both arms in 1993.
Some 2,000 protesters were also arrested outside the clinic during summer-long demonstrations in 1991.
Monnat characterized the case as a witch hunt begun by former Attorney General Phill Kline, an ardent abortion foe, and continued by his successors out of personal and political pressure.
"This case was designed by an anti-abortion politician and pursued by other politicians who were too afraid to do the right thing," Monnat told jurors in his closing argument.
"It has been ... open season on doctors who provide abortions to women," he added. "Is that America?