In 1974 a phenomenon called M74 was discovered in Atlantic salmon (Salmo salar). M74 is a reproductive disorder that has several negative consequences for the health of salmon and high mortality in the offspring. M74 occurs due to a deficiency of thiamine which is a vitamin in the B-vitamin complex. The reasons for why thiamine deficiency occurs have not yet been determined but several hypotheses have been discussed. This study aimed to investigate how length, weight and condition factor are affected by the incidence of M74, and whether the incidence varies between wild and farmed stocks. The study involved digitizing paper charts where the power company Vattenfall has documented information on the fitness of Atlantic salmon since the 1970s at Norrforsen in Umeå. The fitness-related factors length, weight and condition factor were analyzed using a paired t-test and the correlation between them was analyzed using Kendall’s correlation test. The results showed a certain relationship between weight and length and the incidence of M74. Females that produced a high proportion of offspring with M74 symptoms were slightly shorter and lighter but had the same condition factor compared to females that produced a lower proportion of offspring with M74 symptoms. The results obtained contradict previous studies where condition factor has shown a connection to M74. The reason for these different results is not clear and therefore further in-depth analyses are required.