OBJECTIVES: This study assessed per patient direct medical costs and indirect work loss of diagnosed interstitial cystitis (“IC”) patients from an employer's perspective. Treatment pattern of IC was also assessed. METHODS: Patients under age 65 with at least one IC diagnosis (n=749) were drawn from a de-identified, administrative database of approximately two-million beneficiaries that includes medical, drug, and disability claims for 1999-2002. A 2:1 matched non-IC control sample was randomly selected based on matching demographic characteristics (i.e. age, gender, region of residence). Annual costs and comorbidities were compared between IC and the non-IC samples descriptively. A multivariate two-part regression model was applied to estimate IC excess medical costs and indirect work loss costs while adjusting for observed patient demographics and comorbidities. All costs were adjusted to 2002 USD using Consumer Price Index (“CPI”). Intent-to-treat approach was adopted to profile treatment patterns of IC. RESULTS: An average IC patient had 130% higher direct medical costs ($3756) and 80% higher indirect costs ($725) than a non-IC patient. Compared with non-IC patients, IC patients had higher diagnostic prevalence of prostatitis (Relative Risk (“RR”)=40.0, P<0.05), endometriosis (RR=7.4, P<0.05), vulvodynia (RR=6.9, P<0.05), chronic pelvic pain (RR=5.8, P<0.05), and urinary tract infections (RR=5.1, P<0.05). IC patients were also more likely to suffer from depression (RR=2.8, P<0.05) and anxiety (RR=4.4, P<0.05). Seventeen percent of IC patients received pentosan polysulfate sodium, the only approved oral drug indicated for IC, within the first two months following the initial diagnosis. Approximately half of IC patients received no drug treatment within two months following the diagnosis. CONCLUSIONS: IC is a costly disease associated with increased risk of comorbidities. IC patients are commonly untreated.