Transition diseases result in considerable economic losses for dairy producers. The purpose of this study was to evaluate the technical consequences of subclinical ketosis (SCK), their economic impact on dairy farm, and the profitability of prevention strategies used in practice. Data from current literature was collected and summarized, and used to model the impact of different incidences (20–40–60%), and its effect on milk production (loss of 5–10% for 60 d), fertility (decrease of 25–50% for 120 d), and increased risk of displaced abomasum, clinical ketosis, metritis and the culling risk of 6, 3.6, 2 and 3.7 times, respectively. Two systematic prevention strategies applied to all cows at calving were used: propylene glycol (PG) with a total cost of €12/cow and a 47% reduction of incidence; or a slow-release monensin bolus (MON) with a total cost of €30/cow and a 60% reduction of incidence. Four simulations were carried out at 2 milk prices (€300 and €360/t): 1) a control without SCK incidence; 2) with SCK (40% incidence, a 10% loss of milk production and a 50% decrease in fertility); 3) with SCK and PG; and 4) with SCK and MON. The SCK impact was evaluated in a farm of 300 dairy cows with average 12,000 L/cow/yr and average technical performance indexes for dairy farms in Spain, using a dairy farm stochastic dynamic model (www.dairyfarm.es; Calsamiglia et al., 2018). The cost per case was €339, ranging from €277 to €373 among incidences. Economic losses due to decreased milk production (64%) were larger that losses attributed to reduced reproductive performance (36%). The PG (€63) was a more profitable strategy compared with MON (€33). Although the cost of the case was similar across incidences, when the incidence was reduced (fewer cases) or milk price decreased, the economic return of prevention treatment was lower. Subclinical ketosis has important effects on cow performance and farm profitability. The adequacy and type of prevention strategy depends on the SCK incidence, the cost of treatment and the price of milk.