The exterior of Dr. Welby's office was the same building used as the Cleaver family home on Leave It to Beaver (1957) with only Welby's shingle as the new addition to the set.
The series "Marcus Welby, M.D." ran on the ABC television network, the last created, and typically the least successful of the big three television networks, until Welby came along. Welby became the most successful series ever to run on ABC, up until that time. By the late 1970s, Welby had been a major contributor to ABC becoming the number one television network, and attracted producers who had previously shunned ABC, in favor of CBS and NBC. By being a #1 and top-10 show, a major hit by any measure, Welby permanently changed that dynamic for ABC.
Spoofed in Mad Magazine as "Makeus Sickby, M.D.".
Elena Verdugo, who played Welby's nurse/assistant Consuelo on all but one episode of the series, got her start as a "femme fatale" in 1940s Westerns and horror films. Her most prominent role before Welby was as Wolf Man Larry Talbot's love interest in The House of Frankenstein.
Season 6, Episode 5, The Outrage (1974), about a gay child molester, sparked real outrage by gay activists who complained the show was perpetuating anti-gay stereotypes, which prompted picketing across the country. This led to 17 ABC TV affiliates refusing to air a network episode in response to protests for what's believed to be the first time. Many sponsors refused to advertise during the edition's broadcast.