The etiology of disorders may be attributable to multiple causal factors simultaneously. This study sought to investigate how frequently, and which causes coexist in patients with iron deficiency. All patients who applied to the Iron Deficiency Outpatient Clinic between January and December 2021 were included in this cross-sectional study. The causes of iron deficiency were extracted from patient files. Analyses were conducted on the entire population as well as three subgroups: women of reproductive age, postmenopausal women, and males. Numbers and frequencies of causes of iron deficiency were calculated. The subgroups were compared using the Jamovi software. The study sample comprised a total of 331 patients. Women of reproductive age were the majority of patients admitted to the clinic (86.7%, n=287). Men represented 6.3% of the sample (n=21), and postmenopausal women accounted for 7.0% (n=23). The mean ages were 37.6±9.05, 49.2±15.49 and 57.8±10.84 years, respectively. The overall sample's rate of multiple iron deficiency causes coexisting was 33.5% (n=111) and the subgroups showed similar frequencies for the coexistence of multiple causes. Statistically, the number of simultaneous multiple causes varied between subgroups (χ2=118, df=10, p<0.001). Heavy menstrual bleeding and nonsteroidal anti-inflammatory drug use were the most common dual causes of multiple coexisting conditions (n=46, 41.4%). In terms of the number of causes, the coexistence of two causes of iron deficiency in women was notable, whereas the coexistence of three causes in males was remarkable. Furthermore, it has been found that some patients have up to five coexisting causes of iron deficiency. Some iron deficiency causes may coexist, and this must be taken into account for the effective management of iron deficiency.