  We report unfiltered photometry of the first confirmed outburst of the AM CVn
system SDSS J012940.05+384210.4 during 2009 December. At its brightest the star
was magnitude 14.5, 5.4 magnitudes above mean quiescence. Although the first
part of the outburst was not observed, six remarkable rebrightening events were
observed during the course of the outburst. Forty-one days after the outburst
was detected, the star was still 1.7 magnitudes above quiescence. Superhumps
were observed during the outburst with a peak-to-peak amplitude of 0.06 mag and
Psh = 37.9(2) min. We also used archival data to show that another AM CVn
system, SDSS J124058.03-015919.2, has also undergone at least one outburst,
with an amplitude of ~4.6 magnitudes.
