FORTUNE — It’s no big secret that the vast majority of venture capitalists are men. But that vastness is even a bit larger than I had expected.

Following yesterday’s news that Jennifer Fonstad and Theresia Gouw were stepping down as partners with DFJ and Accel Partners, respectively, in order to launch their own firm, we decided to begin researching exactly how many partner-level female VCs there really were.

To do so, we first asked PitchBook for a list of all U.S.-based VC firms that had raised at least one fund of $200 million or more since 2009. In total there were 92 such firms, which had raised approximately $66.3 billion for 138 funds over that time period.

Then we began researching each firm, trying to determine how many senior partners were women. This proved a bit tricky, since not all firms use the same terminology. When in doubt, we looked for the most senior “layer” of investment professionals, be they “general partners” or “managing partners” or “partners” or “investment directors.” We excluded anyone who also served in CFO or COO positions, unless they also represented the firm on portfolio company boards. We also used current staffing, rather than who may have been with the firm at the time the actual fund was raised (e.g., Gouw wasn’t included as part of Accel Partners). This was science with a bit of educated art thrown in.

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What we found was that only 23 of the 542 partner-level VCs I identified were female. That works out to just 4.2%, and actually would be a bit lower if we could figure out how many partner-level VCs work at Sequoia Capital (the firm declined to disclose, except to acknowledge that none of them are women).

For context, this 4.2% figure even trails the paltry 4.6% of female CEOs among the Fortune 500.

Of the 92 firms, only 17 had even one senior female partner. Of those 17, just five firms had multiple senior female partners. Of those five, only one firm (Scale Venture Partners) had at least three senior female partners.

Also worth noting that we also tried to examine firms based outside of the U.S., but were unable to find sufficient “team” data on too many of the firms within our sample. For those firms we were able to track, however, we found that the percentage of senior female partners was 4.8%.

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