The proloculus diameters were analyzed in 15 samples of 200 individuals each of the agglutinated foraminifer Trochammina inflata from five salt marsh localities in Germany, Denmark and Sweden. Accumulations of dead specimens from the uppermost centimeter of sediment between the roots of salt marsh halophytes include microspheric and, as revealed by statistical analyses, two classes of megalospheric individuals. These size classes are consistent with the occurrence of three generations in a trimorphic life cycle as has been described in several other foraminiferal taxa, and they support the interpretation of a biologically trimorphic life cycle in Trochammina inflata. The three size classes of proloculi correlate with: agamonts (microspheric tests), schizonts (smaller megalospheric tests) and gamonts (larger megalospheric tests). This interpretation, however, has not been confirmed by studies on cultivated specimens. Other factors that may cause the bimodal size distribution of the megalospheric proloculi are discussed. The sample means of the agamonts range from 16.1–22 μm, those of the supposed schizonts from 28.6–34.2 μm and those of the supposed gamonts from 36.5–41.7 μm. The proportions of the three generations are used to infer long-term life cycles in time-averaged assemblages. Samples from Bottsand (Kiel Bight, Germany) contain particularly high proportions of schizonts, indicating that schizogony may be the dominant or sole mode of reproduction at the latter sites. Proportions of gamonts are relatively high in the Heden saltmarsh (Swedish west coast) and in the remaining localities, indicating a higher incidence of the dimorphic cycle, relative to the trimorphic cycle. A varying importance of the respective mode of reproduction results in differing proportions of reproductive products, agamonts, gamonts and schizonts in the sediment. Previous investigations have focussed on trimorphism in tropical environments; herein, we present an example from temperate supralittoral-semiterrestrial habitats subject to strong fluctuations in water content, temperature and salinity.