Objectives: Particulate matter (PM) is an important component of air pollution and may contribute to the development or exacerbation of allergic diseases. The purpose of this study was to evaluate the associations between 24-hour indoor PM concentrations and the prevalence of asthma, allergic rhinitis/allergic conjunctivitis, and atopic dermatitis among adolescents participating in the Polish Mother and Child Cohort Study (REPRO_PL). Material and Methods: Indoor PM_2.5 and PM₁₀ concentrations were measured over a 24-hour period using portable air-sampling pumps. Information on adolescent health was obtained from questionnaires and medical records. Additional assessments included spirometry, fractional exhaled nitric oxide (FeNO) measurement, and skin prick testing. Unadjusted comparisons and multivariable logistic regression analyses were performed for 172 participants with complete data on the analyzed outcome and exposure variables. Results: Particulate matter 10 showed a positive but statistically non-significant association with asthma (OR = 2.22, 95% CI: 0.88–5.57, p = 0.09). No statistically significant associations were observed between indoor PM_2.5 or PM₁₀ concentrations and allergic rhinitis/allergic conjunctivitis or atopic dermatitis. Conclusions: Further studies involving larger populations and repeated or longer-term air measurements are needed to clarify the relationship between indoor particulate matter exposure and allergic diseases. Int J Occup Med Environ Health. 2026;39(5)