Experimental studies suggest ceramides may play a role in insulin resistance. However, the relationships of circulating ceramides and related sphingolipids with plasma insulin have been underexplored in humans. We measured 15 ceramide and sphingomyelin species in fasting baseline samples from the Strong Heart Family Study (SHFS), a prospective cohort of American Indians. We examined sphingolipid associations with both baseline and follow-up measures of plasma insulin, HOMA of insulin resistance (HOMA-IR), and HOMA of β-cell function (HOMA-B) after adjustment for risk factors. Among the 2,086 participants without diabetes, higher levels of plasma ceramides carrying the fatty acids 16:0 (16 carbons, 0 double bond), 18:0, 20:0, or 22:0 were associated with higher plasma insulin and higher HOMA-IR at baseline and at follow-up an average of 5.4 years later. For example, a twofold higher baseline concentration of ceramide 16:0 was associated with 14% higher baseline insulin (P < 0.0001). Associations between sphingomyelin species carrying 18:0, 20:0, 22:0, or 24:0 and insulin were modified by BMI (P < 0.003): higher levels were associated with lower fasting insulin, HOMA-IR, and HOMA-B among those with normal BMI. Our study suggests lowering circulating ceramides might be a target in prediabetes and targeting circulating sphingomyelins should take into account BMI.