Myelodysplastic syndromes (MDS) incidence is unclear because of historical lack of population‐based registration and possibly because of underdiagnosis. We conducted a study to evaluate completeness of MDS registration in the Seattle‐Puget Sound region of the Surveillance, Epidemiology, and End Results (SEER) program—which has reported the highest rates among the SEER registries since mandatory reporting of MDS began in 2001. We identified incident MDS cases of any age that occurred within a nonprofit healthcare system in western Washington State in 2005 or 2006 through the local SEER registry or by relevant diagnostic code followed by medical chart review to classify these patients as unlikely, possible, or definite/probable MDS. We calculated age‐standardized incidence rates for all identified MDS cases and for case groups based on identification method, and we summarized medical histories of the MDS patients. MDS incidence in our study population was estimated as 7.0 per 100,000 person‐years in 2005–2006 when combining MDS cases identified by SEER and definite/probable cases identified by chart review, which was similar to the rate of 6.9 reported by our local SEER registry. The addition of possible MDS cases identified from chart review increased the rate to 10.2 per 100,000. MDS patients frequently had previous cancer diagnoses (25%) and comorbidities such as high blood pressure and diabetes. Our investigation suggests that although reporting of confirmed MDS diagnoses in our region appears complete, MDS incidence is likely underestimated because of omission of cases who are symptomatic but do not receive definitive diagnoses.

© 2010 Wiley‐Liss, Inc.