The evolving representation of Atlantic tropical cyclones (TCs) in the ERA40 reanalysis dataset from 1957 through 2001 is analyzed using metrics of intensity and the three-dimensional cyclone phase space. On average, TC structural representation within the ERA40 has shifted two Saffir-Simpson (SS) categories over the 45 years. Thus, a category three TC during 1957--1971 is comparable in ERA40 representation to a category one during 1988--2001. Further, the ERA40 does not statistically distinguish between category three and four hurricanes within any given tercile. It is also found that less than seven millibars of ERA40 MSLP separate a category one from a five TC, mean ERA40 MSLP does not always decrease with increasing SS category, and not all SS categories are statistically significant with regard to MSLP. It follows that great caution should be exercised when using ERA40 to diagnose long-term trends in TC structure and intensity within the Atlantic.