An endocrine disruptor, the fungicide fenarimol, was investigated regarding its effects on reproduction and hormone (ecdysteroid) levels in the deposit-feeding amphipod Monoporeia affinis. In addition, the influence of food shortage, both by itself and in combination with fenarimol, on reproduction was examined. Field-collected amphipods were exposed in flow-through microcosms during the period of sexual maturation and mating in four treatment series: Control with low food, fenarimol with low food, control with high food, and fenarimol with high food. Fenarimol was added at a concentration of 0.3 mg/L in two pulses/ week. Results show that fenarimol has a negative effect on fertilization rate and male mating ability. Results were supported by a tendency toward delayed male sexual development. Food shortage decreased weight in both sexes and retarded female oocyte development. Higher ecdysteroid levels were recorded in males than in females, and food shortage increased male ecdysteroid levels. No effect of fenarimol exposure on ecdysteroid levels was observed. No synergistic effects of fenarimol and food shortage could be distinguished in any variable examined. Thus, M. affinis was vulnerable to reproductive impairment by fenarimol, with effects on the next generation (i.e., a disturbed sexual development and fertilization ability). Food shortage has negative effects on M. affinis, but it does not enhance the effects of fenarimol.