Allergen-induced anaphylaxis has been suggested as a possible etiology for sudden infant death syndrome (SIDS). Some of the measures recommended for reducing the risk of allergen exposure also are recommended for reducing the risk of SIDS. The purpose of this study is to evaluate possible associations between dust-mite allergen (der p 1) levels within cot (crib) mattresses and established cot mattress risk factors for SIDS. Dust from polyurethane foam was extracted from two regions of used cot mattresses donated by 28 households in Leicester (United Kingdom) and der p 1 allergen levels estimated using a two-site monoclonal antibody system. Infant and cot environment-related factors were determined via parental questionnaire. For the infants' head region of the mattresses, the following associations were independently significant following multivariate analysis: quantity of dust extracted, with older mattresses (p = 0.014); high allergen concentrations (der p 1 per mg dust), with high frequency of minor ailments (p < 0.001) and older infants (p = 0.044); and high total der p 1 content, with high frequency of minor ailments (p = 0.014). There were no independently significant associations between levels of der p 1 in polyurethane foam and the established cot mattress risk factors for SIDS. Although der p 1 accumulates within polyurethane foam of cot mattresses with use over time, this does not provide a valid mechanistic explanation for the established cot mattress-related risk factors for SIDS. There is an association between der p 1 levels of cot mattress polyurethane foam and frequency of minor ailments; additional research is required to establish cause and effect.