Although the dynamics of transmission play an important role in the occurrence of intramammary infection (IMI), they have not been considered in previous models used to estimate the cost of IMI. The bio-economic model described includes within-herd dynamics of pathogen-specific IMI. The model simulated Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli IMI stochastically and estimated the cost of these IMI in a herd of 100 dairy cows in a situation where a quota is applied to milk production. A Reed-Frost model was used for S. aureus, S. uberis, and S. dysgalactiae IMI and a Greenwood model for E. coli IMI. Economic analysis was conducted per pathogen for clinical and subclinical IMI. The parameters used in the model were based on the literature and were deemed credible and valid. Median annual incidence of clinical and subclinical IMI for all pathogens varied considerably. This variation was greatest for S. aureus IMI. The annual incidence of IMI in a herd of 100 dairy cows caused by S. aureus varied between 0 and 88 cases, with a median of 5 cases and the 5th and 95th percentiles of 0 to 36 for clinical IMI, and a median of 7 cases with the 5th and 95th percentiles of 0 to 52 for subclinical IMI. In consequence, the average total annual net costs also varied widely for S. aureus IMI. Clinical IMI costs were € 1375, with the 5th and 95th percentiles of 0 to 4716 and subclinical IMI costs were € 1219, with the 5th and 95th percentiles of 0 to 4030. The average annual net cost due to the 4 simulated pathogens combined was € 4896 and varied from € 915 to € 11,287 in a herd of 100 dairy cows. The bio-economic model developed for this study will be utilized as a tool to investigate the economic impact of management of pathogen-specific IMI.