OBJECTIVES:  To evaluate the association of socio-demographics factors and clinical complications at presentation with future medical expenditures in diverticulitis patients. METHODS:  Using the electronic medical records of the Kaiser Permanente Southern California Health Plan, we identified all adults (18+ years) who had acute diverticulitis (incident cases) during 01/01/2007 to 12/31/2011. Prior to diagnosis of the incident event (index date), patients were required to be a health plan member continuously enrolled for ≥ 12 months (baseline period) without evidence of diverticulitis. Through chart review, we captured the following complications during the incident presentation: abscess, intestinal obstruction, pneumoperitoneum, fistula and peritonitis. We identified medical expenditures (2016 USD) associated with inpatient (IP), emergency department (ED) and outpatient (OP) visits during the one year period after the index date. Total expenditure was the sum of IP, ED and OP expenditure. A generalized linear model with log link and gamma distribution was specified which adjusted for the following covariates: age, race, sex, ethnicity, income, insurance type, Elixhauser comorbidity, and clinical complications. RESULTS:  We identified 32,884 incident cases: age (mean ± SD), 59 ± 14 years; 58% female; 68% white. The average adjusted total expenditure was $8,848 (95% CI $8,703 to $8,993). Age, race, ethnicity, income, insurance type and multimorbidity were independently associated with future total expenditure. Each identified complication was associated with significantly higher total expenditure: abscess ($7054, ($6171 to $7936)), intestinal obstruction ($4,433 ($3235 to $5632)), pneumoperitoneum ($4,838 ($4131 to $5546)), fistula ($7,083 ($4359 to $9807) and peritonitis ($7,324 ($3510 to $11137)). CONCLUSIONS:  Presence of complicated diverticulitis was associated with significantly increased expenditure during follow-up. The magnitude of the marginal future expenditure associated with abscess, fistula and peritonitis might offset cost of elective surgical procedures, in patients presenting with such complications.