Urinary 1-hydroxypyrene (1-OHP) has been suggested as an exposure biomarker for polycyclic aromatic hydrocarbons (PAHs). However, it remains unknown whether a first morning urine sample can be used to reflect average exposure. In this paper, we examine intra-individual differences and inter-individual associations between first morning voids and 24-h composite urine samples. The analysis was performed using data collected from 100 adults who had a wide range of PAH exposure due to differences in their occupation, e.g., coke oven workers vs. non-coke oven workers. For each subject, all the urine voids within each of two 24-h measurement periods were collected. Results showed a significant (40% to 62%) intra-individual difference between first morning voids and 24-h urinary 1-OHP concentrations (in ng/ml urine). Creatinine adjustments of 1-OHP concentrations (in micromol/mol urinary creatinine) reduced the intra-individual difference by approximately 10%. Across all the subjects, a high overall correlation (r=0.76) was observed between first morning and 24-h average 1-OHP concentrations. Work environment and sampling season were found to significantly affect the relationship between first morning and 24-h 1-OHP concentrations. An increase of 1 ng/ml of first morning urinary 1-OHP predicted an increase of 0.5 and 0.25 ng/ml of 24-h urinary 1-OHP for coke oven workers and non-coke oven workers, respectively. Data collected in a winter season showed a higher correlation between first morning and 24-h concentrations than data collected in a fall season. Creatinine adjustments did not significantly improve overall correlations between first morning void and 24-h measurements, but increased total variances for 24-h urines explained by first morning urines in coke workers.