Lysine and energy are two nutrients that directly impact litter and subsequent farrowing performance. Genetic selection has increased litter sizes and milk production leading to increased amino acid and energy demands by the lactating sow. Milk production alone results in 70% of the amino acid requirements and 65 to 80% of the energy requirement during lactation. Some sows do not meet the recommended lysine intake levels due to sow-to-sow variation in feed intake. There is no clear understanding of the relationship between lysine and dietary energy during the summer months when intake is decreased, and energy levels are increased. This study evaluated two standardized ileal digestible lysine levels (0.85% and 1.11%) and two energy levels (3183 and 3334 kcal/kg) during lactation. Results indicate that feeding a diet with a greater lysine concentration during lactation reduced feed intake, backfat, and body condition of the sow. Increasing dietary energy immediately prior to farrowing and during lactation did not affect sow feed intake. Sows fed higher dietary energy had increased stillborns and decreased percentage of pigs born alive. However, increased energy improved piglet performance by decreasing pre-wean mortality and increasing litter gain resulting in heavier litter weaning weights. Sows fed a combination of high lysine and high energy had a longer wean to estrus interval compared to those fed high lysine and low energy. These results indicate that energy and lysine inclusion will ultimately need to be balanced by the mixed effects on sow body condition, farrowing performance, and litter performance.