Patients presenting in hospital with symptoms of acute diverticulitis. Acute inflammation of the left-sided colon is confirmed with CT scan or ultrasound in experienced centers and diagnosis is defined according to the "Classification of Diverticular Disease (CDD)". CDD Type 2a, 2b and 3b will be included and then randomized in two groups. Group A will get an early left hemicolectomy 7 to 10 days after admission and initial antibiotic therapy and/or drainage of the abscess. Group B is designated for an elective resection 6 to 8 weeks after dismissal at the earliest and initial conservative treatment and/or after drainage of the abscess. Six weeks after the operation patients of Group A will be asked for their present quality of life with a standardized scoring system (Gastrointestinal Quality of Life Index = GIQLI; Short-form 36 Score = SF-36 Score; Low anterior resection syndrome = LARS Score). Group B (elective resection) will be asked at their readmission prior to elective surgery is done. This survey package will be repeated again 6 to 8 weeks later in both groups. Primary endpoints will be the two GIQLI at the said examination times. Secondary endpoints will be SF-36 score, LARS-score, GIQLI-Domains, anastomosis insufficiency and other complications, mortality and length of hospital stay. Comparisons between the groups are made at the said examination times but also 6-8 weeks after the operation.

Primary endpoints:

Gastrointestinal Quality of Life Index (GIQLI)

Secondary endpoints:

SF-36 score (physical and mental health summary scores), LARS score, GIQLI-domains, anastomosis insufficiency and other complications, exitus and length of hospital stay

Treatment strategy:

A patient is coming into the hospital with acute symptoms of diverticulitis. The diagnosis must then be confirmed either with ultrasound or with a CT scan. After confirmation the patient is asked to be part of the study. At that point of time the patient does not know his randomization. After the patient's approval and signed consent the patients will bei informed about the further procedure and the appointment of surgery. Questionnaires will now be filled out and antibiotical treatment starts. If necessary a radiological intervention (drainage) is performed.

Is the patient is randomized into Group A he will get early left hemicolectomy immediately up to a maximum of 2 days after 7-10 days lasting initial conservative or interventional treatment (e.g: antibiotics, analgesics, drainage). If the patient is in Group B he will receive an elective left hemicolectomy 6 to 8 weeks after 7-10 days lasting initial conservative or interventional treatment (e.g: antibiotics, analgesics, drainage).

Reassessment of the questionnaires will bei done in both groups. Group A will be asked 6-8 after surgery and again 6-8 weeks after the second reassessment.

Group B will be asked 6-8 weeks after discharge (directly before surgery) and again 6-8 weeks after surgery.

The aim of the study is to evaluate the outcome and quality of life in patients receiving early surgery versus elective resection of the left-sided colon in acute complicated diverticulitis and chronic recurrent diverticulitis with acute exacerbation.

Inclusion Criteria:

• Informed consent to participate in the study
• CDD Type 2a, 2b: acute complicated left-sided diverticulitis
• CDD Type 3b: relapsing diverticulitis without complications (>2 episodes within 2 years)
• Acute presentation
• Inflammation located in the left-sided colon
• Inflammation is CT proven or ultrasound confirmed from experienced radiologists

Exclusion Criteria:

• < 18 years
• Pregnancy
• BMI > 55kg/m2
• Current colorectal carcinoma in the left-sided colon
• Oral and/or intravenous corticosteroid
• Ongoing chemotherapy
• Status post left hemicolectomy
• Patients who cannot take care of themselves at home or are unable to follow instructions
• Patients who are not fit for surgery (anesthesia, expert knowledge from specialists) and will not benefit from surgery