OBJECTIVES:   Examine the association between degenerative disk disease (DDD) and patient length of stay (LOS) and total payments among patients who underwent lumbar fusion surgery. METHODS:   Patients who underwent an anterior lumbar interbody fusion (ALIF), posterior lumbar fusion (PLF) or transforaminal or  posterior lumbar interbody fusion (T/PLIF) surgery over the time period from 2006 - 2009 in the Thomson Reuters MarketScanÒDatabases were identified.  These patients were examined for evidence of degenerative disk disease (DDD).  Multivariate regressions were used to examine the association between DDD and LOS and total payments, while controlling for patient age, sex, type of insurance coverage, and type of procedure. RESULTS:   Of the 28,647 patients who underwent lumbar fusion surgery, 7,230 had an ALIF, 16,374 had a PLF, and 5,043 had a T/PLIF.  13,340 (46.57%) of the sample had a comorbid diagnosis of DDD (ICD-9 code 722.6x, 722.51, 722.52).  However, the majority of these patients were also diagnosed with an additional comorbid back problem - only 1,911 (6.67%) were diagnosed with "stand alone" DDD.  Compared to patients without DDD, patients who had DDD and no additional comorbid back problem were found to have $5,557 lower total payments (P<0.0001) and 0.17 shorter LOS (P<0.0001), after controlling for patient characteristics and type of procedure.  In contrast, patients with DDD and an additional comorbid back diagnoses were found to have $4,876 higher total payments and 0.07 longer LOS compared to patients without DDD. CONCLUSIONS: DDD is an uncommon sole clinical rational for lumbar fusion surgery.  Patients who underwent a ALIF, PLF or T/PLIF with "stand-alone" DDD had significantly lower total payments and significantly shorter LOS, while patients with DDD and additional back diagnoses had significantly higher total payments and longer LOS compared to patients who underwent an ALIF, PLF, or T/PLIF without a comorbid diagnosis of DDD.