The society said professionalism needs to be adopted across the industry. If individual companies increase their professionalism, their effectiveness will be restricted by the need to compete against less professional organisations, which might focus on keeping prices low.
The call has come in the wake of research into professionalism and IT success by a BCS working party, which included senior people from IBM and the Institution of Electrical Engineers.
The work has drawn on BCS discussions at senior level with the Office of Government Commerce, the Office of the E-Envoy and other government departments, and the society's involvement in the new Skills Framework for the Information Age, which was launched by several industry organisations last month.
"Whether we like it or not, neither the IT industry nor those involved in it are perceived as being professional," said BCS deputy chief executive Colin Thompson. "Much of the performance of both is seen as decidedly unprofessional.
"Professionalism is key to improved performance - but not just the professionalism of IT practitioners.
"Delivering quality products and services requires focused professionalism across all aspects of an organisation," he said.
"Quality products and services are the result of professional organisations employing competent professional people in all functions, working to professional standards and processes."
Key areas for professionalism include technology and business knowledge, customer and supplier relationship management, and staff recruitment and management, Thompson said.
This demands a professional ethos and culture across an organisation, because piecemeal approaches are unlikely to be effective, he said.
"If competent people are poorly led, they are likely to produce poor results," he said. "Under-pricing or over-promising at the bid stage is likely to impact on the quality of the final service, however professional the individuals involved.
"Good processes do not, in themselves, guarantee good products. Good managers with competent people working with good processes may fail if the culture of the organisation is poor.
"Even success may be perceived as failure if customer expectations are unrealistic."
Thompson said quality issues could only be fully resolved by the whole industry working together. He drew parallels with the building industry, which started tackling similar issues of poor perceptions of quality with an industry-wide programme after two damning reports in the 1990s.
Organisations seeking to be professional should recruit staff who are properly qualified in terms of their professional attitude, competence and skills, Thompson said.
"It is also essential that such organisations should seek to further develop these professional attributes by encouraging staff to achieve appropriate independent accreditation."
He emphasised the need for entire organisations to embrace professionalism.
"The use of practitioners who are properly qualified for the work they are required to undertake will play an important part in improving the quality of products and services," he said. "It is essential that this should be in the context of the required level of overall corporate capability and professionalism."