OBJECTIVE To identify the effect of stoma site marking on stoma-related complications. METHODS The study sample included 639 individuals with stomas who were followed up in a stomatherapy unit in Turkey between January 1, 2017, and June 20, 2021. Researchers collected patient data from nursing records. Data were evaluated using number, percentage, χ2, and logistic regression tests. RESULTS Of the individuals with stomas, 60.6% (n = 387) were men, and 72.6% (n = 464) had a cancer diagnosis. Their mean age was 60.16 (SD, 14.81) years. The stoma site was marked preoperatively in of 67.1% of patients (n = 429), and 17.1% (n = 109) developed stoma-related complications. The complication rate was higher in individuals with unmarked stoma sites (25.7%; P =.000), emergency surgeries (25.0%; P =.006), colostomies (23.9%; P =.042), and permanent stomas (28.3%; P =.002). The three most common complications were peristomal skin problems (56.9%), mucocutaneous separation (13.8%), and edema (9.2%). CONCLUSIONS The incidence of stoma-related complications in the postoperative period was higher in individuals with unmarked stoma sites. The authors recommend that stoma and wound care nurses mark the stoma site in individuals for whom stoma creation is planned.