The rate of sexually transmitted infections (STIs) has soared in China. Yet, there is no universal consensus about the accuracy of the syndromic approach to STI management. This study aims to compare the syndromic approach with laboratory tests. A randomly selected sample of market vendors in eastern China (n = 4510) was recruited and assessed for the five most common STIs (Chlamydia trachomatis infection, gonorrhoea, genital herpes [herpes simplex type 2, HSV-2] syphilis and trichomoniasis [female only]). Symptom-based assessments made by physicians were compared with laboratory tests. Laboratory test results were used as the gold standard for the comparisons. The overall sensitivity of physician symptom-based assessment was about 10%; sensitivity was lower for males (1.6%) than for females (17.2%). The sensitivity of physician assessments for those who reported STI symptoms was relatively higher (36.7%) than for those who reported no symptoms (5.1%). More than half (54.37%) of the participants were diagnosed with STI of trichomoniasis. For the other four types of STIs, physicians correctly identified only <10% of the positive cases. The study detected a low sensitivity of STI diagnosis made by physicians in an Eastern city of China. The failure in the detection of asymptomatic patients remains one of the limitations of the syndromic approach.