The assessment of cognitive function in early life has recently become an issue for consideration in long-chain polyunsaturated fatty acid (LC-PUFA) supplementation studies. This article reviews the various means by which such assessment has been done in past LC-PUFA supplementation studies and provides some background on recent advances in the measurement of infant cognition that may need to be considered when planning or designing future supplementation studies. These include (i) consideration of the specificity of LC-PUFA effects on cognition, (ii) inclusion of multiple tasks or levels of measurement as outcome measures, and (iii) a stronger emphasis on developmental processes in the design of such studies.