The effect of temperature and salinity on the larval development of the common spider crab Maja brachydactyla (Balss, 1922) were studied in the laboratory. Larvae were reared at different salinities (0–45) at constant temperature, and under six different combinations of temperature (18 and 21°C) and salinity (30, 35, and 40). The survival and developmental time from newly hatched zoeae to the megalopa stage and from megalopa to the first juvenile stage was quantified; the 24 h median lethal salinity (LS50) for first zoeal stage was calculated. Dry mass (DM), elemental body composition (Carbon, Hydrogen, Nitrogen) and carbon: nitrogen ratio (C:N) were determined in both starved and nourished zoeae. The lower and upper LS50 for M. brachydactyla first zoea in 24 h were 19.9 and 56.0, respectively; similar to other marine stenohaline brachyuran larvae. The megalopa stage was reached in a salinity range from 30 to 40. The highest survival rates to the first juvenile stage were observed at salinity: 35 and temperature: 21°C. Salinity was the key parameter for the survival to first juvenile, whereas the temperature had a higher effect over the duration of the larval development. The greatest loss of DM in starving and nourished zoeae was observed at low salinity (25). No differences were found in DM or C:N during the megalopa stage. The culture and ecological implications of the salinity tolerance of M. brachydactyla larvae are discussed.