The current standard Swedish infection prophylaxis in colorectal surgery is intravenously administered cefuroxime and metronidazole. this combination is well studied. The disadvantages of the regimen is "collateral damage" resulting from treatment with a cephalosporine and that the combination also serves as the first line of treatment for abdominal surgical infections.

Serval Swedish surgical departments have for some years used a combination of orally administered trimethoprim-sulfamethoxazole and metronidazole.

The combination is economical and believed to be effective but hitherto the outcome have not been properly researched.

The aim of this study is to compare the efficacy of these two regimens in the prevention of infection after elective colorectal surgery.

Inclusion Criteria:

• Age >= 18 years
• Planned clean/clean-contaminated colorectal resection will be performed
• Understand spoken and written swedish language

Exclusion Criteria:

• Hypersensibility to the test or control drug
• Severe liver failure
• Blood dyscrasia
• Ileus or gastric retention
• Current visceral perforation
• Current treatment with antibiotics
• Current treatment with steroids
• Cytotoxic or radiation therapy within 4 weeks of the planned operation
• Active IBD (inflammatory bowel disease)
• Incapability to swallow tablets
• Other study interfering with this study
• Current pregnancy
• Bad regulated diabetes
• Current enterocutaneous or colocutaneous fistula