Background: Mycoplasma and Ureaplasma species are considered part of the normal genitourinary microbiota; however, when present in excessive amounts, they may become pathogenic and cause symptoms such as dysuria, vaginal discharge, and lower abdominal pain. Due to the lack of specific clinical manifestations, these infections may remain undiagnosed or be misidentified as other inflammatory conditions. Disseminated infection caused by Mycoplasma and Ureaplasma is rare. Case Presentation: A 27-year-old female presented with progressive pelvic pain and was initially discharged without a definitive diagnosis. The disease subsequently worsened, and laboratory as well as imaging studies revealed a complicated pelvic infection with concurrent pregnancy. Despite surgical intervention and intensive treatment, the patient died due to severe pelvic purulent inflammation, sepsis, septic shock, and multiple organ failure. Multiplex PCR testing was positive for Mycoplasma genitalium (+), Mycoplasma hominis (+), Ureaplasma parvum (+), and Ureaplasma urealyticum (+). The final clinical diagnosis was consistent with the pathological findings. Conclusion Pelvic disease caused by Mycoplasma and Ureaplasma often presents with nonspecific symptoms, making differential diagnosis challenging. In this case, concurrent pregnancy and the use of analgesic medication may have obscured the disease progression. Comprehensive clinical assessment, close observation, appropriate diagnostic testing, and contact tracing with epidemiological investigation are essential in suspected sexually transmitted infections.