The objective was to investigate how differences among hospitals in the shift from in-patient care to day surgery and a reduced hospital length of stay affect the sick-leave period for female patients surgically treated for breast cancer. All women aged 18-64 who were diagnosed with breast cancer in 2000 were selected from the National Cancer Register and combined with data from the sick-leave database of the National Social Insurance Board and the National Hospital Discharge Register (N = 1834). A multi-factorial model was fitted to the data to investigate how differences in hospital care practice affected the length of sick-leave. The main output measure was the number of sick-leave days after discharge during the year following surgery. The confounders used included age, type of primary surgical treatment, whether or not lymph node dissection was performed, labour-market status, county, and readmission. Women treated with breast-conserving surgery had a 54.7-day (-71.9 < or = CI(95%) < or = -37.5) shorter sick-leave period than those with more invasive surgery. The day-surgery cases had 24.3 (-47.5 < or = CI(95%) < or = -1.1) days shorter sick-leave than those who received overnight care. The effect of the hospital median length of stay (LOS) was U-shaped, suggesting that hospitals with a median LOS that is either short or long are associated with longer sick-leave. In the intermediate range, women treated in hospitals with a median LOS of 2 days had 22 days longer sick-leave than those treated in hospitals with a mean LOS of 3 days. This is possibly a sign of sub-optimising.