BACKGROUND: Around 20% of 1- to 4-month-old infants cry for long periods without an apparent reason. Traditionally, this was attributed to gastrointestinal disorder ('colic'), but evidence shows that just 5% of infants cry a lot because of organic disturbances; in most cases, the crying is attributable to normal developmental processes. This has led to a focus on the impact of the crying on parents. Parental vulnerabilities influence how parents evaluate and respond to the crying and predict adverse outcomes. By developing evidence-based services that support parents, this study was designed to take the first steps towards national health services that enhance the coping and well-being of parents whose babies excessively cry. Related aims were to improve these infants' outcomes and how NHS money is spent. OBJECTIVES: To develop a novel intervention package to support parents of excessively crying infants and to examine the feasibility of delivering and evaluating it in the NHS. DESIGN: Stage 1 of this study aimed to (1) complete a literature review to identify example support materials, (2) obtain parents' guidance on the support needed when a baby cries excessively, together with their evaluation of the example materials, and (3) develop a support package based on the results. Stage 2 aimed to (1) recruit 60 parents whose babies were currently excessively crying, (2) assess parents' and NHS professionals' willingness to complete a study of the support package, (3) measure the use and evaluation of the package components, (4) estimate the package component costs and (5) provide evidence on the feasibility and methods for a large-scale trial. SETTING: Primary health care. PARTICIPANTS: Stage 1: 20 parents of previously excessively crying infants and 55 health visitors (HVs) or specialist community public health nurses (SCPHNs). Stage 2: 57 parents of currently excessively crying infants and 124 HVs/SCPHNs. INTERVENTIONS: The support package included a website, a printed booklet and a programme of cognitive-behavioural therapy-based sessions delivered to parents by a qualified practitioner. MAIN OUTCOME MEASURES: (1) Demographic data, (2) figures for parents' use of the package components and continuation in the study, (3) parents' and HVs'/SCPHNs' ratings of the package components and suitability for NHS use, (4) questionnaire measures of parental well-being and infant health and (5) costs. RESULTS: Most parents (95%) accessed the website or printed materials and half (51%) attended the practitioner sessions. All 52 parents and 85% of HVs/SCPHNs providing data would support the inclusion of the package in the NHS. It was associated with reduced parental frustration, anxiety, depression, reported infant crying and contacts with health professionals and increased knowledge about crying. Methods for a full trial and figures for the cost of excessive infant crying for the NHS and each package element were identified. LIMITATIONS: No control group was included. Most of the recruited parents were white, well educated and in stable relationships. CONCLUSIONS: Parents and HVs/SCPHNs recognise the need for NHS provisions that support parents of excessively crying babies and consider the materials developed to meet that need. A full-scale randomised controlled trial is feasible and desirable. TRIAL REGISTRATION: Current Controlled Trials ISRCTN84975637. FUNDING: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 23, No. 56. See the NIHR Journals Library website for further project information.