OBJECTIVE: To address systematic variations related to the day of the interview in self-reports of alcohol consumption in telephone health surveys. The investigations include temporal clustering effects, prediction of alcohol consumption and variations across days by characteristics of respondents and interviewing period, and sensitivity to variations of measurements instruments. METHOD: Data at baseline collected in Spring 1999 from 2846 participants in a longitudinal probabilistic general-population survey in Switzerland were used. The study is representative for drinkers in Switzerland. Alcohol consumption measures include a 6-month quantity frequency and a 1-week graduated frequency measure. RESULTS: Evidence for systematic variations in self-reports related to the day of interview was found on the graduated-frequency measure even after controlling for sample characteristics. Similar variations on the quantity frequency measure were found, but were no longer significant after statistical control of the sample characteristics. CONCLUSIONS: Statistical inference in alcohol survey research by telephone interviews based on graduated-frequency measures with short reference period may be plagued with errors related to clustering effects of the day of the interview. Temporal aspects of conducting the fieldwork should therefore be accounted for in statistical analysis.