Objective:To investigate epidemiological characteristics of Mycobacterium marinum infection cases in the Dermatology Hospital of Shandong First Medical University from January 2019 to December 2021. Methods:Data were collected from patients with Mycobacterium marinum infection in the Dermatology Hospital of Shandong First Medical University from January 2019 to December 2021. Demographic characteristics, clinical features and prognosis of patients were retrospectively analyzed. Differences between groups were analyzed using t test, Chi-square test and Fisher′s exact test; factors influencing the time to diagnosis (the time from the first appearance of skin manifestations to the diagnosis of Mycobacterium marinum infection in the hospital) longer than 12 months were analyzed using Chi-square test and multivariate logistic regression model, and the odds ratio ( OR) and 95% confidence interval (95% CI) were calculated. Results:From 2019 to 2021, a total of 373 cases of Mycobacterium marinum infection were diagnosed in the hospital, and the number of cases in 2021 was 4.06 times that in 2019; the male-to-female ratio was 1∶1.49, and their age was 54.24 ± 14.04 years. Among the 373 patients, 211 (56.57%) had a history of trauma caused by aquatic products (e.g., fishes, shrimps), of which 51 (24.17%) were stung by sea perch. Skin lesions involved unilateral limbs in 327 (87.67%) patients, only involved the hands or wrists in 188 (50.40%) patients, and 258 (69.17%) had multiple skin lesions. Among the 341 patients with treatment information, 105 (30.79%) were given one antibiotic, 214 (62.76%) received combination treatment with two antibiotics, and 15 (4.40%) were treated with three antibiotics. The response rate was 98.77% (321/325), and the time to diagnosis [ M ( Q1, Q3) ] was 5.03 (3.00, 8.37) months. Multivariate logistic regression analysis indicated higher proportions of males ( OR [95% CI]: 1.95[1.11 - 3.41], P = 0.02), patients aged > 55 years ( OR [95% CI]: 1.82[1.04 - 3.18], P = 0.04), patients with skin lesions only involving hands, arms or lower limbs ( OR [95% CI]: 3.48[1.83 - 6.61], P<0.001) among the patients whose time to diagnosis was longer than 12 months. Conclusions:The number of patients with Mycobacterium marinum infection was increased in the Dermatology Hospital of Shandong First Medical University year by year from 2019 to 2021, and fish sting wounds were the main cause of infection. The most common treatment regimen was the combination of two antibiotics, with a high efficacy profile.