Both environmental fluctuations and physical characteristics of amphibians (e.g., body size, sex, or age class) affect their growth. Eastern Red-backed Salamanders, Plethodon cinereus, are often used as indicators of habitat quality in eastern North American forests. Most of the research concerning growth in this species has focused on the influence of body size, rather than on other external or temporal factors that might affect growth. We performed a mark–recapture study spanning multiple years and seasons to compare the growth of individuals of P. cinereus across temporally variable environmental conditions. Unsurprisingly, the most significant factor affecting growth was body size. Growth also varied seasonally and annually, with greater growth of salamanders during a mild winter and more growth in 2014 than 2013. Sex-age class did interact with yearly fluctuations as evidenced by juveniles, but not adults, having reduced growth in 2014. However, color morph did not have an effect on growth. We concluded that fluctuating environmental conditions, as well as body size, exerted effects on the salamanders' growth. This study adds to our understanding of the factors affecting growth in terrestrial salamanders and provides context for past and future studies of body size and abundance in this ecologically important species.