Phase relations in the Hg–Pd–Se system were studied by the evacuated silica glass tube technique. For kinetic reasons, experiments were performed in the range 350–400 ºC. We present here the 400 ºC condensed isothermal section for the Hg–Pd–Se system, based on literature data and on our experiments. Two ternary phases were known previously: Pd8Hg3Se9, which corresponds to tischendorfite, and Pd2HgSe3. We report here on a third phase, Pd5HgSe. Tischendorfite forms stable assemblages with palladseite (Pd17Se15), tiemannite (HgSe), potarite (PdHg), and with the phase Pd2HgSe3. In turn, Pd2HgSe3 forms stable assemblages with PdSe2 (orthorhombic), palladseite (Pd17Se15), tischendorfite (Pd8Hg3Se9), and tiemannite (HgSe). The phase Pd5HgSe, stable near the Pd-rich corner of the system, forms stable assemblages with metallic Pd, PdHg (potarite), palladseite (Pd17Se15), and other Pd-rich binary palladium selenides. Palladseite forms limited solid-solution and dissolves up to 4.15 at.% Hg at 350 ºC. This solid solution forms stable assemblages with Pd8Hg3Se9, PdSe2, and HgPd (potarite). There are no joins involving HgSe (tiemannite) and binary Pd selenides.