The as-cast structure of permanent mould and high-pressure die-castings of the AlMg$_{5}$Si$_{2}$Mn alloy is investigated by differential scanning calorimetry, microhardness measurements, transmission electron microscopy, and energy dispersive X-ray analysis. Inside the $\alpha$-Al grains, the curved plate-like precipitates are detected for both alloys. Examination of these precipitates reveals a number of features, such as follow: (i) the composition of the precipitates is very close to the stoichiometric Mg$_{2}$Si compound; (ii) precipitates are aligned along dislocations; (iii) the precipitate density is much higher for the high-pressure die-castings, where the $\alpha$-Al matrix contains more dislocations than in permanent mould castings; (vi) precipitates lie inside the $\alpha$-Al grains, where they are randomly distributed. Precipitates are not observed among the Mg$_{2}$Si lamellas. Most likely, these precipitates are $\beta^{''}$-phase, and the mechanism of their formation is the heterogeneous nucleation on dislocations.