The direct cost in the US of breast-conserving treatment at the current 25% usage of this treatment (as a percentage of all cases) and at a 24.3% rate of outpatient surgery (the rate in the US in 1990) was $1,439,483,489. At an outpatient rate of 70% (the plausible upper limit) the direct costs were $1,359,459,362. If breast-conserving treatment was used in 50% of all cases then the costs were $1,509,955,755 (24.3% outpatient surgery rate) and $1,349,907,500 (70% outpatient surgery). The direct cost of all patients having mastectomy if 15% have reconstructive surgery was $1,470,849,600; if 25% of patients have reconstructive surgery then the cost was $1,606,628,000. Including home care after outpatient surgery and the value of lost production due to radiation treatment the total cost of breast-conserving treatment (when 25% of all patients have this treatment and 24.3% have outpatient surgery) was $1,504,224,047; an incremental cost of $33,374,447 compared to all patients having mastectomy (at a 15% rate of reconstructive surgery). At a 50% rate of outpatient surgery breast-conserving treatment realised an incremental saving of $8,105,738. At a 70% rate the incremental saving was $40,386,038. However, these calculations do not include the indirect costs of mastectomy; it is likely that if the indirect cost of mastectomy is included, the incremental cost of breast-conserving treatment would be lower (or the savings due to its use larger).