Aim: To date, the search for diagnostic markers of atopic dermatitis (AD; also known as atopic eczema) is ongoing. Such markers should help to identify allergic inflammation and help control the severity of the disease. Our aim was to analyse the diagnostic significance of eosinophilic cationic protein (ECP) in AD patients. Methods: People with AD and those without (‘healthy’) were examined. AD patients were grouped by age: 18–40 years and >40 years old. All AD patients were tested for allergic inflammation makers. Statistical processing of the obtained results was carried out using variational statistics and the Statistica v10. Results: A total of 24 patients with AD and 10 healthy people were included. In the AD group, there were 12 people aged 18–40 years, and 12 people aged >40 years of age. With increased age, there was a decrease in the number of people with the extrinsic form of AD indicated by a high level of IgE, and an increase in the number of people with intrinsic AD indicated by a low level of IgE (odds ratio [OR]: 2.92; 95% confidence interval [CI]: 1.83 to 4.65; p<0.001). Both the form of AD and the total serum IgE level were dependent on the age of the patient (OR: 5.72; 95% CI: 2.52 to 13.94; p<0.001). Simultaneously, when the severity of AD increased, ECP level increased (OR: 4.26; 95% CI: 2.01 to 9.05). Conclusion: We suggest the level of ECP in people with AD could be used as an indicator for allergic inflammation, as the levels of ECP increased with the severity of the disease. The level of ECP did not depend on the age of the patient or the the form of AD.