The Hg $\frac{L}{K}$ x-ray intensity ratio in the decay of ${\mathrm{Tl}}^{204}$ has been determined with proportional and scintillation counters, using Ag $K$ x rays for intercomparison of detector efficiencies. Beta rays were stopped before they entered the detectors. The shape of the bremsstrahlung spectrum under the x-ray peaks was determined with ${\mathrm{Cl}}^{36}$ beta rays. The result is $\frac{{I}_{L}}{{I}_{K}}=0.52\ifmmode\pm\else\textpm\fi{}0.02$. The mean $L$ fluorescence yield of Hg following electron-capture decay of ${\mathrm{Tl}}^{204}$ then is ${\overline{\ensuremath{\omega}}}_{L}=0.40\ifmmode\pm\else\textpm\fi{}0.05$, if the $\frac{L}{K}$ capture ratio is 0.42 as measured by Joshi and by Leutz and Ziegler. The partial $L$-shell fluorescence yield of Hg following ${K}_{\ensuremath{\alpha}}$ x-ray emission was measured as ${\ensuremath{\omega}}_{\mathrm{KL}}=0.41\ifmmode\pm\else\textpm\fi{}0.02$ from $K$ and $L$ x-ray coincidences. The partial $L$-shell fluorescence yield of Hg following $L$ capture only of ${\mathrm{Tl}}^{204}$ is ${\ensuremath{\omega}}_{\mathrm{LL}}=0.39\ifmmode\pm\else\textpm\fi{}0.06$, as determined by the same method.