Derek Longmuir (born 19 March 1951, Edinburgh, Scotland) was the Scottish drummer and a founding member of the 1970s pop group, Bay City Rollers. His elder brother, Alan Longmuir, played bass guitar in the group.
Longmuir was born at Simpson Memorial Maternity Pavilion Hospital, in Edinburgh. He appeared on each of the band's nine studio albums through to 1981. He retired from the music industry in the early 1980s and trained as a nurse working at Edinburgh Royal Infirmary.
In 2000, Longmuir was sentenced to 300 hours community service after admitting possessing child pornography. Due to the controversy, he was fired from his job at the Infirmary although he was later readmitted to the nursing register. Despite his guilty plea, he maintained that the offending materials did not belong to him but were left behind by an acquaintance. Longmuir claimed he pleaded guilty in hope of avoiding a "media circus".
In an interview in the Sunday Herald on 7 May 2000, Longmuir's foster son, Jorge Loureiro, claimed that Longmuir was innocent and had been framed by an obsessed American fan he had befriended, with discs having been sent to his home anonymously days before he was arrested.