Munson opened his practice in 1967. He was arrested in 1969 for performing an abortion on a 19-year-old patient. Munson challenged his conviction, winning in circuit court. The state appealed, and the South Dakota Supreme Court ruled against him. He appealed this decision, which was rendered moot by Roe.
In 1973, Munson discharged a 28-year-old patient after an incomplete abortion. She died of sepsis three days later. Munson was charged with manslaughter. Seventh Circuit Judge Merton Tice, Jr. instructed the jury to acquit, saying that the state's case was inadequate because prosecutors could not prove that Munson intended harm to his patient. Then-Attorney General Bill Janklow contended that Munson's culpability was clear.